SCIENCE 


3 

o 


QRMEMB 


CO 


GIFT  OF 
PROF.  W.B.  RISING 


SPECTRUM  ANALYSIS. 


LESSONS 


IN 


CHEMISTRY 


BY 


WILLIAM  H.  GREENE,  M.D., 

P!   3FESSOR  OF  CHEMISTRY  IN  THE  PHILADELPHIA  CENTRAL  HIGH  SCHOOL,   ETC. 


PHILADELPHIA: 
J.    B.    LIPPINCOTT    &    CO. 

LONDON:    15   RUSSELL   STREET,  COVENT    GARDEN. 
1884. 


0 


Copyright,  1884,  by  J.  B.  LIPPINCOTT  &  Co. 


TABLE  OF   CONTENTS. 


PAGE 

I. — Introduction — Chemical  Phenomena 7 

II. — Hydrogen 16 

III. — Oxygen — Combustion  ........  23 

IV. — Composition  of  Water — Chemical  Laws  and  Theories  .         .  32 

V. — Laws  of  Combination — Atomic  Theory         ....  38 

VI. — Properties  of  Water — Potable  and  Mineral  Waters      .         .  45 

VII. — Chemical  Nomenclature — Ozone — Hydrogen  Dioxide  .         .  50 

VIII.— Chlorine— Chlorides 57 

IX.— Hydrochloric  Acid— Acids— Salts 62 

X. — Bromine — Iodine — Fluorine          ......  68 

XL— Sulphur— Hydrogen  Sulphide 73 

XII.— Sulphur  Dioxide— Sulphur  Trioxide 79 

XIII.— Sulphuric  Acid 82 

XIV.— Sulphates 87 

XV.— The  Atmosphere   .         .     - 91 

XVI. — Ammonia  and  its  Compounds        ......  97 

XVII. — Ammonium  Compounds 101 

XVIII.— Nitrogen  Monoxide— Nitric  Oxide 104 

XIX.— Nitrogen  Peroxide— Nitrogen  Pentoxide      .         .         .         .108 

XX.— Nitric  Acid 112 

XXL— Nitrates 116 

KXIL— Phosphorus— Hydrogen  Phosphide 119 

J>  XIII. — Oxides  and  Acids  of  Phosphorus           .....  123 

XXIV.— Arsenic— Compounds  and  Tests 128 

XXV. — Antimony      ..........  134 

XXVI.— Boron 137 

XXVII.— Silicon— Glass -140 

XXVIII.— Carbon 144 

XXIX.-Oxides  of  Carbon 150 

XXX.— Carbonates 156 

XXXI.— Carbon  Disulphide— Cyanogen 162 

XXXII. — Hydrocyanic  Acid — Cyanides 166 

XXXIII.— Carbonyl  Compounds .171 

XXXIV. — Compounds  of  Carbon  and  Hydrogen  (1) 

Methane  and  Saturated  Hydrocarbons       .          .          .          .175 

237556 


4  TABLE    OF    CONTENTS. 

LESSON  PAOE 

XXXV. — Compounds  of  Carbon  and  Hydrogen  (2) 

Petroleum — Unsaturated  Hydrocarbons     ....  181 
XXXVI. — Compounds  of  Carbon  and  Hydrogen  (3) 

Aromatic  Hydrocarbons — Elementary  Analysis       .         .186 

XXXVII.— Methyl  and  Ethyl  Alcohols— Alcoholic  Beverages       .         .  192 

XXXVIII.— Alcohols— Glycols— Glycerin 197 

XXXIX.— Simple  Ethers .  201 

XL. — Aldehydes — Carbon  Acids — Compound  Ethers    .         .         .  206 

XLI. — Fatty  Acids — Saponification 212 

XLIL— Lactic,  Oxalic,  Tartaric,  and  Citric  Acids   .        .         .         .  218 

XLIIL— Hydrates  of  Carbon .220 

XLIV.— Benzol  Derivatives,  Phenol,  Nitrobenzol,  Aniline        .         .  226 
XLV. — Benzol  Derivatives,  Benzole,  Salicylic,  Gallic,  and  Tannic 

Acids — Camphors — Indigo       ......  230 

XLV  I.— Natural  Alkaloids 236 

XLVIL— Metals— Spectrum  Analysis 241 

XLVIII.— Metallic  Compounds— Specific  Heat 246 

XLIX. — Lithium — Sodium — Potassium 250 

L.— Silver 257 

LI. — Calcium — Strontium — Barium 265 

LIL— Lead 272 

LIII. — Magnesium — Zinc — Cadmium 277 

LIV.— Copper 283 

LV.— Mercury       .         .         .         .         .         .         .         .         .         .290 

LVL— Bismuth  and  Gold 295 

LVII.— Aluminium          .        . 301 

LVIII.— Iron  and  its  Metallurgy 307 

LIX. — Iron  and  its  Compounds 315 

LX.— Cobalt— Nickel— Manganese 319 

LXI. — Chromium  and  Tin 325 

LXII.— Platinum  and  its  Allied  Metals 331 

LXIIL— The  Chemistry  of  Life 334 

APPENDIX. 

Crystallography— Hints  for  the  Preparation  of  Experiments  .         .         .341 

Index                                                                                                                 .  347 


ADVICE   TO   TEACHERS. 


T  IE  object  of  a  limited  course  in  chemistry  is  not  to  make  chemists  of  the 
pup  Is,  but  to  teach  them  what  chemistry  is,  what  it  has  accomplished,  and 
wha-  it  may  accomplish.  The  study  of  science  can  be  made  attractive  only 
by  :  rousing  natural  curiosity  as  to  the  cause  of  natural  phenomena,  and  no 
gre;  ter  mistake  can  be  committed  than  to  endeavor  to  make  the  facts  of  chemistry 
dep  ndent  upon  its  theory.  It  is  true  that  here  and  there  an  exceptional 
pup  I  may  grasp  that  theory  and  acquire  the  science;  but  even  in  such  cases 
no  pecial  interest  is  developed,  while  to  the  more  practical  the  subject  be- 
con!  ,>s  both  foolishness  and  a  stumbling-block. 

T  le  successful  teacher  of  chemistry  is  not  only  thoroughly  familiar  with  his 
sen  ice;  he  loves  it.  It  is  not  enough  that  he  has  read  several  text-books  on 
che  listry ;  he  must  be  practically  acquainted  with  all  the  phases  of  the  facts 
wit  i  which  he  deals,  and  must  have  at  least  a  general  knowledge  of  the  liter- 
atu  e  of  the  subject.  His  endeavor  will  then  be  to  impart  to  his  pupils  some 
par  of  his  own  enthusiasm. 

C  lemistry  is  peculiarly  a  study  of  observation,  and  it  should  be  taught  as  it 
has  been  developed, — first  by  the  careful  examination  of  facts,  then  by  the 
thei  retical  explanations  suggested  by  those  facts.  By  new  experiments  the 
intt  :est  of  the  pupil  is  at  once  awakened,  and  will  not  flag  during  the  consid- 
eration of  the  theory  which  explains  the  experiments. 

The  pupil  is  not  to  suppose  that  certain  compounds  are  without  impor- 
tance, but  is  to  understand  rather  that  only  the  more  important  and  more 
prac  tical  can  be  considered  in  the  time  devoted  to  study. 

AA  hile  the  time  has  passed  when  valuable  research  can  be  conducted  with 
ine>  pensive  apparatus,  a  comparatively  extended  course  on  chemistry  can  be 
illustrated  at  little  cost.  Every  teacher  of  chemistry  should  have  some 
knowledge  of  glass-blowing,  and  some  mechanical  ingenuity  to  adapt  the 
sam  2  apparatus  to  various  purposes.  Such  skill  is  readily  acquired  by  prac- 
tice. 

3225  SANSOM  STREET,  PHILADELPHIA, 
1st  May,  1884. 


1* 


THE  DECIMAL  SYSTEM  OF  WEIGHTS  AND  MEASURES, 
AND  THE  CENTIGRADE  SCALE  OF  THE  THER- 
MOMETER, ARE  USED  IN  THIS  BOOK. 


CENTIGRADE    FAHRENHEIT 
SCALE.  SCALE. 


1  Metre           =  39.370708  inches. 

300° 

572° 

1  Centimetre  =    0.39370 

200° 

360° 

1  Millimetre  =    0.03937 

1  Inch            =    2.539954  centimetres. 

100° 

212° 

OUNCES  TROY               POUNDS 

90° 
80° 

194° 

176° 

=  480  GRAINS.      AVOIRDUPOIS. 

1  Milligramme   =         0.000032            0.0000022 

70° 

158° 

1  Centigramme  =         0.000321            0.0000220 

60° 

140° 

1  Decigramme    =         0.003215            0.0002204 

1  Gramme           =         0.032150            00022046 

50° 

122° 

1  Decagramme    =         0.321507            0.0220462 

40° 

104° 

1  Hectogramme  =         3.215072            0.2204621 

1  Kilogramme    =       32.150726            2.2046212 

30° 

86° 

1  Gramme  =  15.4323  grains. 

20° 

68° 

10° 

50° 

1  Grain                    =    0.064799  grammrs. 

0° 

32° 

1  Oz.  Troy                =  31.103496        " 

—10° 

14° 

1  Lb.  Avoirdupois  =    0.453495  kilogrammes. 

—17.8° 

0° 

1  Cubic  Centimetre  of  water  at  0°  weighs  1 

gramme. 

—20° 

—2° 

To  convert  centigrade  degrees  into  Fahrenheit 

—  30° 

—40° 

—40° 

Water  boils. 


Water  freezes. 


degrees,  multiply  by  9,  divide  by  5,  and  add  32°. 
To  convert  Fahrenheit  degrees  into  centigrade 
degrees,  subtract  32°,  then  multiply  by  5,  and 
divide  by  9. 


Mercury  freezes. 

A  dull  red  heat  is  about  500°  centi- 
grade, or  950°  Fahrenheit. 

A  high  red  heat  is  about  1000°  C., 
and  a  white  heat  about  1500°. 


LESSONS  IN   CHEMISTRY. 


LESSON    I. 
INTRODUCTION. 

Cl<  "mistry  is  the  science  which  studies  the  differences  of  different 

kinds  of  matter. 

.  Substance, — Matter  occupies  space,  and  can  be  measured 
an<  weighed.  The  different  kinds  of  matter  constitute  so  many 
dii  erent  substances,  which  are  distinguished  from  one  another  by 
gei  eral  properties,  such  as  color,  relative  weight,  hardness,  etc., 
an«i  no  two  substances  can  be  alike  in  all  properties. 

Some  substances  are  capable  of  existing  in  the  three  possible 
sta.es,  as  solid,  liquid,  and  gas.  Water  is  the  most  common 
ex;  mple  of  such  a  substance;  by  the  action  of  more  or  less  heat 
it  i  an  be  converted  at  pleasure  into  steam,  liquid  water,  or  ice. 
However,  if  we  strongly  heat  a  piece  of  wood  or  some  sugar,  these 
substances  will  not  be  melted  into  liquids  or  changed  to  vapor,  but 
wiL  be  transformed  into  entirely  different  kinds  of  matter,  from 
wh  ch  we  cannot  again  obtain  the  original  substance. 

1!.  Physical  Changes. — We  all  know  that  water  is  capable  of 
existing  in  many  forms:  mist,  fog,  rain,  frost,  snow,  sleet,  and  ice 
all  represent  the  same  substance,  and  we  know  that  these  forms 
may  change  one  into  another  while  the  nature  of  the  substance 
remains  unaffected.  The  salt  water  of  the  ocean  differs  from  the 
fresh  water  of  the  rivers  which  flow  into  it,  only  because  the  sea- 
water  contains  salt  and  other  forms  of  matter ;  but  these  substances 
are  not  water.  If  salt  water  be  boiled,  and  a  plate  or  other  cold 
surface  be  held  in  the  steam  given  off,  drops  of  water  will  condense 

7 


8  -   ^ESSQN^LSr    CHEMISTRY. 


on  tl^p;ia^abxwiir?)e  fonto.be  perfectly  fresh.  The  changes 
which  convert  ice  into  water,  or  water  into  steam  or  ice,  are  called 
physical  changes,  because  the  nature  of  the  substance  is  not 
affected ;  a  little  more  heat,  or  a  little  less,  changes  the  water  into 
steam  or  ice,  or  the  steam  or  ice  back  again  to  water. 

3.  Chemical  Changes, — Water  may,  however,  undergo  other 
changes,  in  which  its  nature  is  altered  and  new  substances  are 
produced. 

Let  us  fill  a  test-tube  with  water,  and,  closing  the  open  end 
with  the  thumb,  invert  it  in  a  small  vessel  of  water.  Then  we 
wrap  a  morsel  of  sodium  (see  §  414)  about  as  large  as  a  pea,  in  a 
small  piece  of  wire  gauze,  twist  around  this  a  wire  which  may 
serve  as  a  handle,  and  now,  raising  the  tube  so  that  its  mouth  is 
just  below  the  surface  of  the  water,  we  push  the  gauze  under  the 
edge  of  the  tube  (Fig.  1).  A  small  piece  of  sodium  must  be  used, 


FIG 


for  the  experiment  is  often  ended  by  a  little  explosion,  which 
might  break  the  tube  if  a  large  piece  were  taken.  As  soon  as  the 
water  touches  the  sodium,  bubbles  of  gas  rise  to  the  surface  and 
are  collected  in  the  tube.  If  the  latter  be  not  quite  filled,  the 
gauze  may  be  withdrawn,  perfectly  dried  by  holding  it  in  a  flame, 
and  another  piece  of  sodium  introduced,  so  that  the  tube  shall  be 
quite  filled  with  gas.  When  this  is  accomplished,  we  may  raise 
the  tube  from  the  water,  still  carefully  holding  it  bottom  upwards, 


INTRODUCTION. 


and  on  introducing  into  it  a  lighted  match  or  taper  the  gas  will 
take  fire,  but  will  extinguish  the  taper,  which  will,  however,  be 
re 'ighted  by  the  burning  gas  as  it  is  withdrawn  (Fig.  2). 

We  shall  presently  learn  that  this  gas, 
which  is  called  hydrogen,  does  not  come 
from  the  sodium,  nor  does  it  contain  any 
so  lium ;  it  must  therefore  be  produced 
from  the  water,  and  that  portion  of  the 
later  which  has  yielded  the  hydrogen 
ni  ist  be  completely  altered  in  its  nature. 
T  le  change  is  called  a  chemical  reaction. 

4.  Elements   and  Compounds.— If 
w  iter  is  thus  capable  of  yielding  another 
si  bstance    produced    wholly    from    the 
w  tter,  we  must  believe  that  water  is  a 
cc  tupound  substance,  composed  of  more 
tl  an  one  kind   of  matter.     Of  the  in- 
numerable forms  of  matter  with  which 
w  !  are  familiar,  all,  excepting  compara- 
tively few,  are  compounds,  and  by  vari- 
ous means  may  be  converted  into  simpler 
fo  -ms. 

Chemists  are   acquainted  with   about 
sixty-eight  substances   which  they  have  been  unable  to  change 
in  o  more  simple  forms.     These  substances  are  called  elements. 

5.  Mercuric  oxide  is  a  heavy,  red  powder.      We  introduce  a 
sn  all  quantity  of  this  powder  into  a  test-tube,  and  heat  it  in  the 
flame  of  a  spirit-lamp  or  Bunsen  burner  (Fig.  3).     We  will  first 
notice  that  its  color  darkens ;  but  this  change  is  only  physical,  for 
if  we  remove  the  tube  and  allow  it  to  cool,  the  original  color  is 
restored.     If,  however,  we  continue  to  heat  it,  in  a  short  time  a 
bright  mirror  forms  on  the  glass  in  the  cooler  part  of  the  tube : 
we  now  light  a  match,  allow  it  to  burn  for  a  moment,  and  then 
blow  it  out,  so  that  it  may  still  retain  a  spark  of  fire;  on  intro- 
ducing this  spark  into  the  tube  it  at  once  bursts  into  flame,  and 
the  match  is  relighted.     The  experiment  may  be  repeated  a  num- 


- 


FIG.  2. 


10 


LESSONS    IN    CHEMISTRY. 


ber  of  times,  extinguishing  the  match  and  relighting  it.  When 
we  have  sufficiently  studied  this  phenomenon,  we  may  examine  the 
tube,  and  we  will  find  that  the  mirror  in  the  interior  is  composed 
of  little  globules  of  metallic  mercury  ;  we  may  shake  them  out  and 
unite  them  in  one.  The  gas  which  has  been  given  off,  and  which 
causes  such  brilliant  combustion,  is  called  oxygen.  The  mercuric 

oxide  was  a  compound 
body.  By  the  aid  of 
heat  we  have  separated 
it  or  decomposed  it  into 
two  other  substances, 
— mercury  and  oxygen. 
Mercury  and  oxygen 
are  elements ;  chemists 
have  not  been  able  to 
convert  either  of  them 
into  other  substances 
of  simpler  nature. 

6.  Sulphur  and  cop- 
per are  also  elements. 
We  all  know  the  yellow 
color  and  brittleness  of 
sulphur,  and  the  red 
color  and  flexibility  of 
copper.  We  will  put 

into  a  test-tube  like  that  used  in  the  last  experiment  a  few  small 
pieces  of  sulphur,  and  on  top  of  them  some  copper  turnings  or  a 
bunch  of  copper  wire.  We  heat  the  tube  ;  the  sulphur  melts,  and 
presently  begins  to  boil ;  but  in  a  few  moments  we  notice  that  the 
copper  becomes  very  hot,  much  hotter  than  the  portion  of  the 
tube  which  contains  only  sulphur.  A  chemical  phenomenon  is 
taking  place,  and  the  chemical  action  develops  great  heat.  When 
the  experiment  has  terminated,  we  allow  the  tube  to  cool,  break  it, 
and  find  that  it  no  longer  contains  copper,  and  unless  we  have 
used  too  much  sulphur  we  will  find  that  the  latter  also  has  dis- 
appeared. In  the  place  of  the  sulphur  and  copper  there  is  a  black, 


FIG.  3. 


INTRODUCTION.  11 

brittle  substance  which  results  from  the  chemical  union  of  the 
tw<  elements.  This  substance  is  called  copper  sulphide. 

1  n  our  first  experiment  we  have  seen  the  decomposition  of  a 
compound  ;  in  the  second  we  have  caused  the  combination  of  two 
elements. 

if  we  were  to  carefully  collect  and  weigh  all  of  the  oxygen  and 
ni(  -cury,  we  would  find  the  weight  exactly  equal  to  that  of  the 
me -curio  oxide  from  which  they  were  obtained.  If  we  make  the 
sec  jnd  experiment  in  a  long  tube  so  that  no  sulphur  vapor  may 
esc  ipe,  the  weight  of  the  tube  will  be  the  same  whether  it  contain 
sulphur  and  copper  or  the  copper  sulphide  resulting  from  their 
uu  on.  Nothing  is  lost  or  gained  in  either  combination  or  decom- 
po  ition. 

L  Chemical  Combination  is  not  Mixture, — Mercuric  oxide 
is  tot  a  mixture  of  oxygen  and  mercury,  nor  is  copper  sulphide  a 
mi  iture  of  copper  and  sulphur.  We  may  grind  the  last  two  sub- 
st;i  ices  to  the  finest  powders  and  mix  them  together,  but  in  this 
mi  iture  we  can  by  the  aid  of  a  microscope  distinguish  the  parti- 
cles of  each  substance.  No  microscope  would  enable  us  to  detect 
sulphur  and  copper  in  the  black  copper  sulphide.  Since,  how- 
evt  r,  we  can  separate  the  oxygen  from  the  mercury,  as  we  have 
seen,  and  the  sulphur  from  the  copper,  we  must  believe  that  the 
ele  nents  still  exist  in  their  compounds.  What  is,  then,  their  real 
coi  dition  ? 

3.  Molecules. — We  know  that  under  certain  conditions  any 
substance  may  change  its  volume.  When  a  piece  of  iron  is  heated 
it  grows  larger ;  when  it  is  cooled  it  becomes  smaller.  We  can- 
not believe  that  the  matter  of  the  iron  actually  increases  in  size 
when  it  is  warmed,  although  it  occupies  a  greater  volume.  We 
can  understand  this  change  in  volume  by  believing  that  there  are 
in  the  iron  spaces  or  pores  which  increase  in  size  when  the  metal 
expands,  and  grow  smaller  when  it  contracts.  These  pores  must 
be  very  small,  for  we  cannot  perceive  them  by  the  aid  of  the 
most  powerful  microscopes.  All  substances  must  be  porous,  and 
we  can  satisfy  ourselves  by  a  simple  experiment. 

We  have  a  glass  tube  about  a  foot  long,  closed  at  one  end,  and 


12  LESSONS    IN    CHEMISTRY. 

near  the  other  blown  out  in  two  bulbs,  and  the  part  between  the 
bulbs  is  rather  narrow  (Fig.  4).  We  pour  water  into  this  tube 
until  it  is  filled  to  the  top  of  the  lower  bulb.  The  water  has  been 
recently  boiled,  to  drive  out  all  of  the  air  which  was  dissolved  in  it. 
We  then  fill  the  remainder  of  the  tube  with  alcohol,  and  cork  it 
tightly ;  the  alcohol,  which  we  have  colored  with  a  little  aniline 
dye,  does  not  at  once  mix  with  the  water,  because  the  latter  is  the 
heavier.  We  now  invert  the  tube,  and  we  see  the  lighter 
alcohol  rise  through  the  water,  and  at  the  same  time  the 
two  liquids  become  thoroughly  mixed.  But  as  they  mix 
we  see  little  bubbles  forming,  and  there  is  presently  a  small 
empty  space  at  the  top  of  the  tube.  This  space  is  not  filled 
with  air ;  for  if  we  put  the  mouth  of  the  tube  under  water 
and  draw  the  cork,  the  water  will  rise  and  fill  the  tube. 
The  mixture  does  not  then  occupy  as  much  volume  as  the 
substances  before  mixture.  We  must  explain  the  experi- 
ment by  saying  that  the  water  and  alcohol  are  porous,  and 
that  the  water  runs  into  the  pores  of  the  alcohol,  and  the 
alcohol  into  the  pores  of  the  water. 

If  substances  be  in  this  manner  porous,  they  must  consist 
of  small  particles  which  are  separated  from  one  another  by 
FlG'  4  spaces.  Both  spaces  and  particles  are  so  small  that  we 
can  never  hope  to  see  them,  but  we  have  reason  to  believe  that 
the  spaces  are  quite  large  in  comparison  to  the  particles  of  matter 
which  they  separate.  These  particles  are  called  molecules,  and  for 
our  purposes  of  study  we  may  consider  that  the  spaces  between 
them  are  perfectly  empty. 

9.  Atoms  and  Molecules. — The  little  particles  of  which  a 
chemical  substance  is  composed  are  called  molecules,  and  we  shall 
learn  reasons  for  believing  that  all  molecules  of  the  same  kind, 
that  is,  of  the  same  substance,  have  the  same  size  and  weight. 

The  kind  of  matter  in  a  molecule  must  be  the  same  as  that  in 
any  quantity  of  the  substance.  If  from  mercury  we  can  obtain 
only  mercury,  the  molecules  of  mercury  must  consist  of  that  ele- 
ment only ;  but  if  from  mercuric  oxide  we  can  obtain  both  mer- 
cury and  oxygen,  the  molecules  of  mercuric  oxide  must  contain 


INTRODUCTION.  13 

boih  of  those  elements.  In  that  case  there  must  be  particles  still 
smaller  than  molecules,  and  to  these  smallest  particles  we  give  the 
name  atoms.  Since  chemists  cannot  separate  oxygen  into  any 
other  substances,  we  believe  that  the  atoms  of  oxygen  are  unalter- 
able by  any  known  force,  be  it  physical  or  chemical ;  and  it  is  the 
sa;iie  with  the  atoms  of  all  other  elements. 

10.  The  atom  is  then  the  ultimate  particle  of  matter,  and  the 
nature  of  an  element  will  depend  upon  the  nature  of  its  atoms. 

11.  A  molecule  may  consist  of  one  or  of  several  atoms:  in  the 
la^  ter  case,  if  the  atoms  be  of  the  same  kind  the  molecule  will  be 
th  it  of  an  element  or  simple  body,  but  if  they  be  of  different 
ki  ids  the  molecule  must  be  that  of  a  compound.     The  molecules 
of  hydrogen  can  contain  only  atoms  of  hydrogen,  and  the  mole- 
cules of  oxygen  must  consist  of  atoms  of  oxygen  only,  but  the 
ni  )lecules   of  water  contain  atoms  of  both  hydrogen   and  oxy- 
g(  n  ;  those  of  copper  sulphide  contain  atoms  of  sulphur  and  of 
ci  pper. 

The  nature  of  a  substance  will  then  depend  upon  the  number 
ai  d  kind  of  atoms  contained  in  its  molecules.  We  have  seen  that 
in  3rcuric  oxide  contains  mercury  and  oxygen  :  let  us  pour  a  little 
nitric  acid  on  some  of  this  red  powder  contained  in  a  test-tube, 
ai;d  warm  the  mixture  over  a  lamp.  The  mercuric  oxide  disap- 
ptars,  and  we  obtain  a  colorless  liquid ;  if  we  pour  this  liquid  into 
a  flat  dish,  and  set  it  aside  in  a  warm  place,  we  will  find  after  a 
time  a  mass  of  white  crystals.  A  chemical  change  has  taken 
pi  ice :  while  dissolving  in  the  nitric  acid,  the  mercuric  oxide  has 
been  converted  into  mercuric  nitrate.  The  latter  body  contains 
mercury,  oxygen,  and  nitrogen,  and  its  molecule  must  consist  of 
atoms  of  each  of  those  elements :  the  new  molecule  is  more  com- 
plex than  that  of  mercuric  oxide,  which  contained  only  two  kinds 
of  atoms. 

12.  Chemical  Affinity. — The  force  with  which  atoms  are  held 
together  is   called  affinity.     Its   energy  is  not  the  same  for  all 
atoms,  and  depends  on  many  conditions.     While  heat  may  aid  in 
the  formation  of  a  compound,  as  with  copper  sulphide,  it  may 
determine  decomposition,  as  with  mercuric  oxide.     Other  forces, 

2 


14 


LESSONS    IN    CHEMISTRY. 


light  and  electricity,  may  act  in  the  same  manner,  in  one  case  pro- 
ducing combination,  and  in  another  decomposition  :  in  every  case 
the  result  depends  upon  the  energy  with  which  the  atoms  of  the 
molecule  are  held  together.  Why  must  we  heat  the  copper  and 
sulphur  before  they  will  combine?  Simply  because  the  atoms  of 
sulphur  hold  strongly  together  in  the  molecules  of  sulphur,  and 
the  atoms  of  copper  in  the  molecules  of  that  metal :  we  must 
therefore  communicate  to  these  molecules  so  much  energy  in  the 
form  of  heat  that  the  atoms  of  sulphur  may  be  sufficiently  loosed 
from  each  other  to  catch  hold  of  the  atoms  of  copper.  Then  in- 
stead of  molecules  containing  atoms  of  sulphur  or  copper  only,  we 
have  others  containing  sulphur  and  copper. 

13.  We  mix  a  small  quantity  of  powdered  cupric  oxide,  a  black 
compound  containing  only  copper  and  oxygen,  with  about  one- 
seventh  its  weight  of  powdered  charcoal,  and  heat  the  mixture 
in  a  test-tube.      When  the  mixture   becomes  hot,  we  see  that 
the  black  color  changes  to  reddish  brown :  after  the  powder  has 
cooled,  we  turn  it  out,  and  find  that  it  is  very  finely  divided 
copper.     We  cannot  heat  the  cupric  oxide  alone  hot  enough  to 
decompose  it ;  but  the  charcoal,  which  is  an  element,  has  a  strong 
affinity  for  the  oxygen,  and  easily  takes  it  away  from  the  copper. 

The  charcoal  and  oxygen  combine  together  and 
form  a  gas  called  carbon  dioxide,  which  passes 
out  of  the  tube.  We  can  prove  that  some 
new  gas  is  formed  during  the  experiment,  for 
if  we  push  a  lighted  match  into  the  mouth  of 
the  tube  while  it  is  being  heated,  the  flame 
will  be  extinguished,  an  effect  exactly  oppo- 
site to  that  which  was  produced  while  heat- 
ing the  mercuric  oxide.  We  then  explain  the 
experiment,  which  is  at  the  same  time  a  com- 
bination and  a  decomposition,  by  saying  that 
the  oxygen  has  a  stronger  affinity  for  the  char- 
coal than  for  the  copper. 

14.  Into  a  jar  or  glass  nearly  filled  with  water  (Fig.  5)  we 
pour  first  a  few  drops  of  a  solution  of  mercuric  chloride,  and  then 


FIG.  5. 


INTRODUCTION.  15 

some  solution  of  potassium  iodide.  At  once  a  pink  or  red  pre- 
cipitate is  formed,  showing  that  a  chemical  change  has  taken 
plice.  Both  mercuric  chloride  and  potassium  iodide  are  color- 
less :  the  first  contains  two  elements,  mercury  and  chlorine,  while 
the  second  also  contains  two,  potassium  and  iodine.  The  chemical 
cl  ange  takes  place  because  the  affinity  of  potassium  for  chlorine, 
ai  d  of  mercury  for  iodine,  is  stronger  than  that  of  potassium  for 
ic  line  and  of  mercury  for  chlorine.  Consequently  both  of  the 
01  iginal  substances  are  decomposed,  and  two  new  substances  are 
f<  rmed,  mercuric  iodide,  which  is  insoluble  (unless  too  much  of 
ei:her  substance  has  been  used),  and  potassium  chloride,  which 
n  mains  dissolved  in  the  liquid.  This  is  an  example  of  double 
<l  -composition,  the  most  common  kind  of  chemical  change.  A 
ci  mparison  will  show  that  it  closely  resembles  the  double  deconi- 
p  tsition  between  sulphur  molecules  and  copper  molecules  already 
explained  (§  12). 

15.  Chemical  affinity  is  not  to  be  regarded  as  a  special  force, 
b  it  only  as  one  form  of  energy ;  it  is  manifested  between  atoms, 
^  liich  it  holds  together  in  the  molecules,  just  as  these  molecules 
a<e  held  together  by  the  force  of  cohesion.     Affinity  depends  not 
o  ily  on  the  kind  of  atoms  between  which  it  is  exerted,  but  on  the 
t(  mperature :  elements  which  have  strong  affinities  for  each  other 
ai  a  given  temperature  may  not  manifest  any  such  affinity  at  other 
temperatures. 

16.  Metals  and  Non-Metallic   Elements.— For  convenience 
of  study  the  elements  are  divided  into  two  general  classes,  metals 
and  non  metals.     The  reasons  for  which  an  element  is  considered 
to  be  a  metal  or  a  non-metal  can  be  understood  when  we  shall 
hive  progressed  farther,  but  we  will  then  learn  that  the  classifi- 
cation is  more   for   convenience  than  because  of  any  absolutely 
special  properties  of  either  class. 

Many  of  the  elements  are  quite  rare,  and  are  seldom  seen  even 
by  chemists ;  others  are  abundant  and  common.  The  names  of 
all  will  be  found  in  the  table  on  page  44. 

The  names  of  the  non-metals  which  we  must  study  are  as 
follows : 


16  LESSONS    IN   CHEMISTRY. 

Hydrogen.  Oxygen.  Nitrogen.  Carbon. 

Sulphur.  Phosphorus.  Silicon. 

Chlorine.  Selenium.  Arsenic. 

Bromine.  Tellurium.  Antimony. 

Iodine.  Vanadium. 

Fluorine.  Niobium. 

Tantalum. 

Boron. 

Because  they  resemble  one  another  in  important  properties,  cer- 
tain of  these  elements  are  classed  together  in  natural  families.  We 
will  be  better  able  to  understand  these  relations  when  we  have 
studied  some  of  the  compounds,  and  have  seen  how  all  of  the 
chemical  changes  through  which  these  compounds  may  pass  can 
be  explained  by  our  theory  of  atoms  and  molecules.  At  the  same 
time  we  will  find  that  our  study  will  greatly  enlarge  and  render 
more  definite  the  ideas  which  we  have  already  acquired. 


LESSON    II. 
HYDROGEN. 

17.  As  we  have  already  seen,  hydrogen  is  one  of  the  elements 
of  water,  of  which  it  constitutes  one-ninth  by  weight.     It  exists 
in  combination  with  other  elements  in  all  animal  and  vegetable 
substances,  in  coal,  and  in  the  natural  oils,  petroleum  and  pitch. 

In  our  first  experiment  (§  3)  we  have  studied  one  method  by 
which  it  may  be  obtained, — the  action  of  the  metal  sodium  on 
water.  That  method  is  unsuitable  for  the  preparation  of  any  but 
very  small  quantities  of  hydrogen  ;  when  it  is  desired  to  prepare 
the  gas  from  water,  steam  is  passed  over  red-hot  iron  or  zinc.  The 
metal  then  combines  with  the  oxygen  of  the  water,  setting  free 
the  hydrogen. 

18.  Preparation. — In  the  laboratory,  hydrogen  is  made  by  the 
reaction  of  zinc  with  hydrochloric  acid  or  sulphuric  acid  diluted 
with  water. 


HYDROGEN. 


17 


We  put  in  the  bottom  of  a  tall  jar  (Fig.  6)  some  small  pieces  of 
very  thin  sheet  zinc,  or 
a  iiandful  of  granulated 
zinc,  and  on  this  pour 
some  hydrochloric  acid. 
A  brisk  effervescence 
bi  gins  ;  when  we  apply 
a  flame  at  the  mouth  of 
tl  e  jar,  the  gas  which  is 
d  sengaged  at  once  takes 
fi  'e,  and  a  large  stream 

0  very  pale  flame  shoots 
it  to  the  air. 

This  gas  is  hydrogen. 

1  :.ydrochloric  acid  is   a 
e  impound    of    chlorine 
a  id  hydrogen  ;  when  it 
a  'is  on  zinc,  that  metal 
d  -ives  the  hydrogen  out 
o:*  its  combination,  and 
uaites  with  the  chlorine, 
f<  rming    a    new    com- 
pound, called  zinc  chlo- 
ride.    We  may  express  the  chemical  change  as  follows: 


BEFORE   THE   REACTION. 

Hydrochloric  acid  +  Zinc 

containing 
Hydrogen  +  Chlorine 


AFTER   THE    REACTION. 

Zinc  chloride  +  Hydrogen 

containing 
Zinc  +  Chlorine 


Dilute  sulphuric  acid  is  usually  employed  instead  of  hydro- 
chloric acid  for  the  preparation  of  hydrogen.  We  may  explain 
the  change  in  a  similar  manner : 

+  Zinc         =         Zinc  sulphate          +  Hydrogen 


Sulphuric  acid 

containing 
Sulphur  +  Oxygen  +  Hydrogen 


=          Zinc  sulphate 

containing 
Sulphur  +  Oxygen  +  Zinc 


It  is  sufficient  to  put  the  zinc  in  a  bottle,  and,  after  pouring  in 
the  dilute  sulphuric  acid,  to  close  the  mouth  of  the  bottle  with  a 
b  2* 


18 


LESSONS    IN    CHEMISTRY. 


FIG.  7. 


cork  through  which  passes  a  tube  for  the  exit  of  the  gas ;  but  it 
is  more  convenient  to  have  a  cork  with  two  holes,  or  a  bottle  with 
two  necks.  Into  such  a  bottle  (Fig.  7)  we  will  introduce  some 
granulated  zinc  that  has  been  made  by  melting 
zinc  and  pouring  it  from  a  little  height  into  a 
bucket  of  water.  Then  we  adapt  to  one  of  the 
necks  of  the  bottle  a  cork  through  which  passes  a 
long  tube  with  a  funnel  at  the  upper  end  ;  the 
lower  end  of  this  tube  must  pass  nearly  to  the 
bottom  of  the  bottle,  so  that  it  may  dip  into  the 
liquid  and  no  gas  may  escape  by  it.  To  the  other 
neck  we  adapt  a  cork  bearing  a  tube  bent  at  right 
angles,  and  this  serves  for  the  passage  of  the  gas. 
Over  the  end  of  this  tube  we  may  pass  a  rubber 
pipe  and  lead  the  gas  wherever  we  wish  it.  We 
now  pour  through  the  funnel-tube  some  sulphuric 
acid  which  we  have  diluted  with  about  five  times 
its  volume  of  water  and  allowed  to  cool,  for  sul- 
phuric acid  becomes  very  hot  when  it  is  mixed  with  water,  and 
we  always  make  the  mixture  by  pouring  the  acid  into  the  water, 
and  not  the  water  into  the  acid.  The  effervescence  shows  us  that 
gas  is  being  disengaged,  and,  after  waiting  a  few  moments  to  allow 
the  hydrogen  time  to  drive  all  the  air  out  of  the  bottle,  we  may 
make  some  experiments  with  our  gas.  These  experiments  will 
make  us  acquainted  with  its  properties. 

19.  Properties  of  Hydrogen, — Hydrogen  is  a  colorless  gas, 
and  has  neither  taste  nor  odor,  as  we  can  determine  by  examining 
it  as  it  escapes  from  the  tube.  It  is  the  lightest  substance  known. 
We  connect  our  gas-generating  bottle  with  the  rubber  pipe,  the 
other  end  of  which  is  passed  over  a  straight  glass  tube,  and  push 
this  tube  up  to  the  bottom  of  a  wide  test-tube  which  is  turned  up- 
side down  (Fig.  8).  In  a  short  time  this  little  jar  is  filled  with 
hydrogen,  for  the  gas  is  so  light  that  it  collects  in  the  jar,  and 
pushes  the  air  down  and  out  at  the  mouth.  We  can  prove  that 
the  jar  is  filled  with  hydrogen,  for  when  we  withdraw  the  tube 
and  introduce  a  lighted  taper,  the  gas  at  once  takes  fire  and  burns 


HYDROGEN. 


19 


FIG.  8.. 


at  the  mouth  of  the  jar  ;  the  taper  is  extinguished  on  entering  the 

gas,  but  is  relighted  as  it  is  drawn  out  through  the 

hxdrogen  flame.     The  hydrogen  is  collected  in  this 

case  by  upward  dry  displacement :  it  displaces  the  air. 

We  again  fill  our  tube  with  hydrogen  in  the  same 

m  inner,  and  taking  another  and  smaller  tube  we  place 

it  alongside  of  the  first,  which  we  carefully  incline 

(h'ig.  9)  more  and  more  until  we  have  poured  all  of 

the  hydrogen  up  into  the  second  jar.    On  introducing 

a   ighted  taper  into  the  latter,  the  gas  takes  fire  and 

burns  with  a  slight  explosion,  for  while  flowing  out  of 

the  first  vessel  it  became  mixed  with  a  little  air. 

On  account  of  its  lightness,  hydrogen  is  often  used 
U  fill  balloons ;  soap-bubbles,  which  may  be  easily 
ID  ide  by  dipping  the  end  of  the  tube  into  suds,  will 
ri-^e  quickly  in  the  air  when  they  are  shaken  from  the  tube. 

A  given  volume  of  hydrogen  is  only  0.0693  as  heavy  as  the 
sa  me  volume  of  air  ?  this  is  expressed  by  saying  that  the  density 
oi  hydrogen  compared  to  air  is 
0.0693 ;  for  equal  volumes,  air  is 
then  14.44  times  as  heavy  as  hydro- 
g(n.  One  litre  4  of  hydrogen  meas- 
ured at  0°  (the  freezing  point  of 
w;iter),  and  under  the  ordinary 
pressure  of  the  atmosphere,  weighs 
0.0895  of  a  gramme. 

20.  The  diffusibility  of  a  gas  is 
its  tendency  to  mix  with  other 
gases :  gases  will  mix  with  one  an- 
other in  this  manner  even  through 
the  pores  of  many  substances  which 
are  sensibly  porous,  that  is,  possess 
pores  large  enough  to  be  seen  by  the  aid  of  a  microscope.  It 
has  been  found  that  the  diffusibility  of  gases  depends  upon  their 
densities.  The  lighter  a  gas  is,  the  more  diffusible  is  it  also,  and, 
on  the  contrary,  the  heavier  gases  do  not  diffuse  as  quickly  as  the 


FIG.  9. 


20 


LESSONS    IN    CHEMISTRY. 


FIG.  10. 


lighter  ones.  Since  hydrogen  is  the  lightest  gas,  we  can  under- 
stand that  it  must  be  the  most  diffusible :  we  allow  a  little  hydro- 
gen to  escape  into  the  air,  and  in  a  few  seconds  it  scatters  through 
all  the  air  in  the  room. 

We  have  arranged  another  tube  through  which  the  hydrogen 
may  escape  from  our  gas-bottle,  and  this  tube  is  drawn  out  so  that 
it  has  a  small  opening  at  which  we  may 
burn  the  gas  if  we  desire.  Close  above 
the  unlighted  gas  escaping  from  this  jet 
we  hold  a  piece  of  paper  (Fig.  10) ;  the 
hydrogen  passes  through  the  paper,  as  we 
prove  by  igniting  it  above,  and  the  flame 
of  the  gas  quickly  sets  fire  to  the  paper 
and  passes  through  to  the  gas  at  the  jet. 

Because  it  is  so  diffusible,  hydrogen 
cannot  be  kept  in  bottles  which  have  the 
smallest  cracks.  It  even  passes  through  hot  plates  of  iron  and 
platinum. 

21.  Hydrogen  is  not  soluble  in  water,  and  it  may  be  collected 
and  kept  over  the  pneumatic  trough.  Gases  which  do  not  dissolve 
in  water  may  be  collected  in  this  manner  :  the  jar  in  which  we 

wish  to  receive  the  gas  is  filled 
with  water  and  inverted  in  a 
trough  near  the  top  of  which  is 
a  shelf  on  which  the  jar  may  rest. 
The  water  will  not  run  out  of  the 
jar  as  long  as  the  mouth  of  the 
latter  is  below  the  surface.  Under 
the  edge  of  this  jar  filled  with 
water  we  pass  the  end  of  the  tube 
from  which  escapes  the  gas  that 
we  wish  to  collect ;  this  gas  bub- 
bles up  through  the  water,  which  it  drives  out  of  the  jar  (Fig. 
11).  If  it  be  desired,  we  can  transfer  the  gas  from  one  jar  to 
'another,  by  first  filling  the  second  jar  with  water,  placing  it  on 
the  trough,  and  then  pouring  the  gas  up  through  the  water  by 


HYDROGEN.  21 

inclining  the  jar  which  contains  it  under  the  edge  of  that  which 
is  10  receive  it. 

22.  Hydrogen  is  the  only  gas  which  conducts  heat.      We  have 
fitted  to  the  ends  of  a  glass  tube  (Fig.  12)  two  tightly-fitting  corks 
through   each   of  which 

pahses  a  smaller  tube, 
an<l  also  a  wire  which 
may  be  connected  with 
an  electrical  battery  ;  the 
tw  >  wires  are  joined  by 

a  t  hin  platinum  wire  which  becomes  heated  red-hot  by  the  electric 
cu  -rent.  We  can  now  pass  any  gas  through  this  tube  and  notice 
th  !  effect  on  the  wire:  we  try  oxygen,  nitrogen,  carbon  dioxide, 
an  I  see  that  the  wire  still  remains  red-hot ;  but  when  we  pass 
h\drogen  through  the  tube,  the  wire  is  cooled  below  redness. 
Tl  e  hydrogen  has  conducted  away  the  heat.  On  account  of  its 
co  i ducting  power,  and  because  it  has  the  property  of  combining 
wi:h  certain  metals,  we  believe  that  hydrogen  is  a  sort  of  metallic 
va  oor.  By  very  great  pressure  and  extreme  cold,  hydrogen  has 
be-jn  converted  into  a  liquid,  and  even  into  a  solid. 

23.  We  have  seen  (§  19)  that  hydrogen  will  burn  in  the  air, 
an  3  that  it  will  not  support  combustion.     When  it  burns,  it  com- 
bines with  the  oxygen  of  the  air,  forming  vapor  of  water  ;  this  is 
tho  sole  product  of  the  combustion  of  hydrogen.     We  may  assure 
ourselves  of  this  by  holding  over  a  jet  of  burning  hydrogen  ajar 
or  any  glass  vessel,  of  which  the  interior  will  rapidly  become  cov- 
ered with  little  drops  of  dew,  and  these  will  soon  unite  together 
and   trickle  down  the  sides  of  the  jar.     This  takes  place  with 
hydrogen  which  has  been  perfectly  dried  by  passing  it  through  a 
tube  containing  calcium  chloride,  or  pumice  stone  wet  with  sul- 
phuric acid    (Fig.    13) ;    both   of  these    substances    remove    all 
moisture  from  gases  with  which  they  come  in  contact. 

If  hydrogen  be  mixed  with  half  its  volume  of  oxygen,  or  about 
three  times  its  volume  of  air,  the  mixture  will  explode  violently 
when  ignited.  For  this  reason  we  must  be  careful  that  all  of  the 
air  has  been  driven  from  the  generating  bottle  before  lighting  the 


22 


LESSONS    IN    CHEMISTRY. 


hydrogen.     We  may  make  the  explosion  harmlessly  by  passing  a 
little  hydrogen  into  a  hydrogen  pistol,  made  of  s.heet  tin,  and,  after 


14. 


FIG.  13. 

corking  the  mouth  of  the  pistol,  ignite  the  mixed  gases  by  holding 
a  flame  to  a  little  hole  at  the  other  end  ;  the 
cork  is  then  driven  out  with  a  loud  noise 
(Fig.  14)  :  we  must  cover  the  hole  with  the 
finger  while  we  are  charging  the  pistol. 
If  we  slip  over  a  small  jet  of  burning 

hydrogen  a  rather  wide  glass  tube  (Fig.  15),  we  will  find  that 
when  the  flame  has  reached  a  certain  point 
in  the  wide  tube  it  begins  to  quiver,  and  a 
more  or  less  musical  tone  is  produced.  The 
tone  may  be  varied  by  using  tubes  of  differ- 
ent lengths :  it  is  caused  by  the  current  of 
air  ascending  the  tube. 

24.  Certain  very  finely  divided  metals 
have  the  power  of  absorbing  hydrogen  so 
rapidly  as  to  become  hot  enough  to  light  the 
gas.  Spongy  platinum  is  such  a  substance  ; 
when  a  small  piece  of  this  very  porous  form 
of  platinum,  tied  by  a  thin  wire  in  the  centre 
of  a  small  brass  ring  (Fig.  16),  is  held  in  a 

jet  of  escaping  hydrogen,  it  becomes  bright  hot  and  the  gas  is 

inflamed.     The  spongy  platinum  should  be  heated  shortly  before 


FIG.  15. 


OXYGEN. — COMBUSTION.  23 

muking  the  experiment.  It  is  not  hard  to  understand  this  phe- 
nomenon, for  when  the  platinum  absorbs 
th  3  hydrogen  the  gas  is  necessarily  re- 
duced to  a  small  volume  in  the  pores  of 
th  3  metal,  and  the  heat  which  keeps  the 
molecules  of  the  gas  at  large  distances 
from  each  other  must  raise  the  tempera- 
tu  :e  when  those  distances  are  diminished 
b\  the  condensation  ;  just  as  the  heat 
w  lich  converts  water  into  steam  reap-  FIG.  16. 

p(  irs  when  the  steam  is  condensed. 

While  hydrogen  combines  with  many  of  the  other  elements, 
th-3  combination  does  not  take  place  directly.  We  have  seen  that 
h(  at  is  required  to  bring  about  the  union  of  hydrogen  and  oxygen. 
II  ydrogen  and  chlorine  combine  under  the  influence  of  light  (see 
§  "*3).  Pure  hydrogen  is  not  poisonous,  but  it  cannot  support 
re  piration  (see  §  33). 


LESSON    III. 
OXYGEN.— COMBUSTION. 

25.  Oxygen  was  discovered  by  Priestley  in  1774.     It  is  the 
nn  st  abundant  element  at  the  surface  of  the  earth  :  it  forms  about 
one-fifth  of  the  atmosphere,  in  which  it  exists  uncombined,  but 
mixed  with  the  element  nitrogen  ;  its  combination  with  hydrogen  is 
water,  and  it  enters  into  the  composition  of  nearly  all  minerals  and 
rocks. 

We  have  seen  (§  5)  that  oxygen  is  produced  when  mercuric 
oxide  is  heated ;  but  this  method  would  be  too  expensive  for  the 
prc  paration  of  large  quantities  of  oxygen. 

26.  Preparation. — The  most  convenient  process  for  obtaining 
oxygen  consists  in  heating  a  compound  of  chlorine,  oxygen,  and 
potassium,  called  potassium  chlorate.     This  is  a  white,  crystalline 


24 


LESSONS    IN    CHEMISTRY. 


substance,  from  which  heat  drives  out  all  of  the  oxygen,  leaving  a 
compound  of  potassium  and  chlorine,  called  potassium  chloride. 

We  put  a  little  potassium  chlorate  in  a  test-tube,  and  heat  it 
rather  strongly  in  the  flame  of  a  spirit-lamp  or  Bunsen  burner. 

It  melts,  and  soon  begins  to 
boil ;  this  boiling  is  the  es- 
cape of  the  oxygen,  as  we 
can  prove  by  pushing  into 
the  tube  a  match-stick  bear- 
ing a  spark  of  fire,  which 
instantly  bursts  into  flame 
(Fig.  17).  The  white  sub- 
stance which  remains  in  the 
tube  after  all  of  the  oxygen 
is  driven  out,  is  the  potas- 
sium chloride. 

When  we  wish  to  make 
and  collect  larger  quantities 
of  oxygen,  we  mix  the  po- 
tassium chlorate  with  about 
one-eighth  its  weight  of 
FIG.  17.  manganese  dioxide,  which 

causes  the   gas  to  be  given 

off"  at  a  lower  temperature,  and  with  less  danger  of  explosion.  The 
manganese  dioxide  is  a  black  powder,  and  is  found  unaltered  after 
the  experiment,  being  simply  mixed  with  the  potassium  chloride  : 
it  helps  the  reaction  because  it  has  an  affinity  for  oxygen  ;  but 
this  affinity  is  so  feeble  that  the  new  compound  which  is  formed 
is  at  once  decomposed,  the  oxygen  being  given  off,  while  the  man- 
ganese dioxide  remains  as  it  was  at  first.  We  may  consider  that 
it  pulls  the  oxygen  away  from  the  potassium  chlorate. 

We  introduce  our  mixture  of  potassium  chlorate  and  manganese 
dioxide  into  a  glass  flask,  to  which  we  adapt  a  tightly-fitting  cork 
bearing  a  tube  for  the  exit  of  the  gas.  Then  we  place  our  flask 
on  some  dry  sand  in  a  little  tin  or  sheet-iron  dish,  which  we  call  a 
-sand-bath,  and  under  this  we  place  our  lamp.  The  sand  becomes 


OXYGEN.—  COMBUSTION. 


25 


hot  and  heats  the  flask  gradually,  and  generally  prevents  cracking 
of  the  glass.     We  may  now  slip  a  rubber  tube  over  the  delivery- 


FIG.  18. 

ti  be  of  the  flask,  and  when  oxygen  begins  to  come  off,  as  we  may 
a>  certain  by  holding  a  lighted  match  near  the  end  of  the  tube,  we 
n  ay  collect  the  gas  in  a  jar  over  the  pneumatic  trough  (Fig.  18). 

As  glass  flasks  often 
b  eak  in  this  experiment, 
w:ien  we  want  many  litres 
ol  oxygen,  we  heat  the 
generating  mixture  in  a 
fl;isk  made  of  sheet  copper 
01  tin  plate ;  to  prevent 
le  iking  in  a  tin  retort,  a 
little  white  lead  is  put  in 
tie  seams  before  they  are 
lapped.  As  little  particles 
of  manganese  dioxide  are 
carried  out  with  the  gas,  we  usually  wash  the  latter  by  making  it 
puss  through  some  water  in  a  wash -bottle.  The  whole  apparatus 
is  shown  in  Fig.  19. 

When  all  of  the  oxygen  has  been  disengaged,  we  remove  the  end 

of  the  tube  from  the  water  in  the  trough  before  taking  the  heat 

from  under  the  flask  :  otherwise  water  would  be  drawn  back  as  the 

retort  cools,  and  would  break  a  glass  flask,  and  the  steam  might 

B  3 


FIG.  19. 


26  LESSONS   IN   CHEMISTRY. 

burst  one  of  tin  or  copper.     This  precaution  is  observed  in  the 
preparation  of  all  gases  made  by  the  aid  of  heat. 

After  filling  several  jars  with  oxygen,  we  remove  them  from  the 
trough  by  passing  a  saucer  under  the  mouth  of  each,  below  the 
surface  of  the  water ;  then  on  lifting  them  out,  the  water  in  the 
saucer  prevents  the  escape  of  the  gas.  We  can  now  turn  them 
quickly  mouth  upward,  still  keeping  covered  with  the  saucer,  and 
we  are  ready  to  study  the  gas. 

27.  Properties, — Oxygen  has  neither  color,  taste,  nor  odor. 
When   freshly  made  from   potassium  chlorate  it  usually  has  a 
smoky  appearance  and  more  or  less  odor,  but  these  are  impurities, 
and  disappear  after  the  gas  has  stood  for  a  time  over  the  pneumatic 
trough.     It  is  a  little  heavier  than   the   air,   its   density  being 
1.1056  ;  one  litre  of  the  gas  at  0°,  and  normal  pressure,  weighs 
1.437  grammes.     It  is  almost  insoluble  in  water.     It  has  been 
converted  into  a  liquid  by  great  cold  and  pressure. 

Oxygen  manifests  energetic  affinity  for  most  of  the  other  ele- 
ments :  it  combines  with  some  of  them  at  ordinary  temperatures, 
and  with  others  by  the  aid  of  more  or  less  heat. 

28.  Combustion.— The   burning  of  wood,  coal,   illuminating 
gas,  oil,  and  other  substances  with  which  we  are  familiar,  is  only 
the  combination  of  those  bodies  with  the  oxygen  of  the  air.    Into 
a  small  tube  closed  at  one  end,  we  have  put  some  ferrous  oxalate, 
made  by  adding  oxalic  acid  to  a  solution  of  ferrous  sulphate,  and 
after  drawing  out  the  open  end  of  the  tube  so  as  to  leave  a  small 
thin   opening,  we  twisted  a  wire  about  the  tube,  and  heated  it 
until  no  more  gas  escaped  at  the  opening  ;  we  then  sealed  the  thin 

end  of  the  tube  by  holding  it 
for  a  moment  in  the  flame. 
The  result  of  this  heating  has 
been  to  decompose  the  ferrous 
oxalate,  leaving  a  very  fine 

powder   of  iron    in    the    tube. 
FIG.  20.  V,T  .       .     .  .        , 

vVe  now  break  this  tube,  and 

shake  out  the  powder,  which  instantly  takes  fire,  falling  in  a  shower 
of  sparks  (Fig.  20),  if  our  tube  has  been  well  prepared.     The  iron 


OXYGEN. — COMBUSTION.  27 

h;,s  combined  with  the  oxygen  of  the  air :  it  has  been  burned  into 
a  substance  called  iron  oxide.  Usually  it  is  necessary  to  heat  a 
cc  mbustible  substance  before  it  will  burn  ;  then  as  soon  as  the 
union  with  oxygen,  or  the  oxidation  as  we  call  it,  begins,  the 
chemical  action  develops  sufficient  heat  to  keep  the  temperature  so 
high  that  the  combustion  may  continue  without  further  aid. 

Only  one-fifth  of  the  air  is  oxygen,  and  we  shall  learn  that  the 
oi  her  gas  with  which  that  oxygen  is  mixed  not  only  does  not  help, 
b  it  prevents  combustion  :  pure  oxygen  should  then  support  com- 
b  istion  much  more  energetically  than  air,  and  we  have  seen  that 
o  :ygen  causes  a  spark  on  a  match-stick  or  a  taper  to  burst  into 
fl  ime. 

29.  We  wrap  a  copper  wire  around  a  piece  of  charcoal,  and 
f;  sten  the  other  end  of  the  wire  in  a  hole  in  a  piece  of  tin  plate 
h.rge  enough  to  cover  the  mouth  of  one  of  our  jars.  After  hold- 
ii  g  the  charcoal  in  a  flame  until  a  corner  of  it  becomes  red-hot, 
VQ  quickly  remove  the  saucer  from  the  jar  and  plunge  into  it  the 
c  larcoal,  which  remains  suspended  (Fig.  21).  Instantly  the  corn- 
bastion  grows  very  vivid,  and,  if  we  have  a  knotty  piece  of  char- 
coal, brilliant  sparks  are  thrown  off.  The  charcoal 
combines  with  the  oxygen  until  all  of  one  or  the  other 
i^  used  up.  The  result  of  the  combination  is  a  gas 
c  illed  carbon  dioxide,  and  if  we  put  a  lighted  taper 
into  the  jar  containing  it,  the  flame  will  be  cxtin- 
«  lished :  we  may  say  that  the  oxygen  has  also  been 
burned,  and  can  serve  for  no  other  combustion  as  long 
as  it  remains  combined  with  the  carbon. 

After  softening  a  steel  watch-spring  by  heating  it  in 
a  flame,  we  twist  it  into  a  coil,  one  end  of  which  we  fasten  in  a 
cork,  and  over  the  other  end  we  slip  the  split  end  of  a  piece  of 
match-stick;  after  lighting  this  we  quickly  introduce  it  into  a 
bottle  of  oxygen  (Fig.  22).  The  flame  heats  the  iron  so  hot  that 
it  can  begin  to  burn,  and  the  oxidation  furnishes  heat  enough  for 
the  combustion  to  continue  :  brilliant  stars  of  burning  steel  shoot 
out,  and  hot  drops  of  iron  oxide  fall  to  the  bottom  of  the  jar,  in 
which  it  is  well  to  leave  a  layer  of  water  to  prevent  breaking. 


28 


LESSONS    IN    CHEMISTRY. 


We  have  prepared  a  deflagrating-spoon  by  fastening  a  small^ 
saucer-like  piece  of  sheet  copper  on  the  end  of  a  straight  copper 
wire.  We  support  this  in  the  hole  in  our 
tin  plate,  and  on  a  little  dry  sand  which  we 
put  in  the  spoon  we  place  a  piece  of  phos- 
phorus (§  177)  a  little  larger  than  a  pea. 
We  light  the  phosphorus — it  takes  fire  very 
easily — and  plunge  the  spoon  into  a  new 
jar  of  oxygen  (Fig.  23).  At  once  a  most 
intense  light  is  produced  by  the  combustion 
of  the  phosphorus,  and  the  jar  becomes 
filled  with  a  white  smoke  of  phosphoric 
oxide,  the  compound  of  phosphorus  and 

oxygen.     After  a  time  this  smoke  dissolves  in  the  layer  of  water, 
which  we  leave  in  the  jar  for  this  experiment  as  for  the  last. 

The  metal  magnesium  burns  very  bril- 
liantly in  the  air :  we  twist  together  half 
a  dozen  ribbons  of  this  metal,  and,  after 
fastening  one  end  in  our  jar-cover,  we 
light  the  other  with  a  match.  On  intro- 
ducing this  into  a  jar  of  oxygen  the  in- 
tensity of  the  combustion  is  dazzling.  A 
white  smoke  of  magnesium  oxide  soon 
settles  in  the  jar,  and  contains  of  course 
the  magnesium  and  oxygen  which  have 
combined  together.  The  jar  is  usually 
broken  in  this  experiment. 

These  experiments  have  been  only  intense  cases  of  what  we 
commonly  call  combustion,  a  phenomenon  which  we  apply  for  the 
production  of  heat  and  light.  The  combustible  substances  ordi- 
narily employed,  such  as  wood,  coal,  illuminating  gas,  wax,  tallow, 
oil,  etc.,  contain  carbon  and  hydrogen ;  charcoal  is  almost  wholly 
carbon ;  these  substances  burn  because  the  carbon  and  hydrogen 
which  they  contain,  unite  readily  with  the  oxygen  of  the  air  when 
the  union  is  started  by  the  aid  of  heat. 

30.  The  brightness  of  the  light  is  not  always  proportional  to 


FIG.  23. 


OXYGEN. — COMBUSTION.  29 

the  amount  of  heat :  we  have  seen  that  the  flame  of  hydrogen  is 
very  pale,  but  it  is  very  hot.  If  we  desire  to  increase  the  heat  of 
a  fire,  we  furnish  the  combustible  with  more  oxygen  by  blowing 
air  into  it  with  a  bellows,  and  we  rake  the  ashes  from  our  coals  in 
order  that  the  oxygen  may  come  in  contact  with  the  hot  carbon: 
it  is  possible,  however,  to  furnish  too  much  air,  if  the  latter  be 
coM,  as  we  see  when  we  extinguish  a  candle-flame  by  blowing  on 
it.  When  we  want  the  most  intense  combustion  possible,  we 
suj  ply  the  burning  body  with  pure  oxygen,  and  the  hottest  flame 
which  we  can  obtain  is  that  of  hydrogen  burning  in  oxygen.  This 
flame  is  that  of  what  is  called  the  oxy hydrogen  blow-pipe,  in  which 
a  t  ibe  through  which  the  oxygen  is  forced  passes  inside  of  another 
tul  e  carrying  the  hydrogen  ;  the  two  gases,  coming  from  separate 
gasholders,  or  caoutchouc  bags,  mix  at  the  opening  of  the  jet  (Fig. 
24 ).  If  they  were  mixed  before  the  moment  of  burning,  the  ap- 


FIG.  24. 


paratus  containing  the  mixture  would  be  burst  by  the  explosive 
un  on  of  the  gases  (§  23).  In  using  the  oxyhydrogen  blow-pipe, 
we  first  turn  on  the  hydrogen,  light  it,  and  then  slowly  turn  on  the 
oxygen  until  we  have  the  hottest  flame.  If  it  be  inconvenient  to 
use  hydrogen,  we  may  substitute  for  it  illuminating  gas,  connect- 
ing by  a  rubber  tube  the  oxyhydrogen  blow-pipe  with  a  gas  fix- 
ture. While  the  oxyhydrogen  flame  is  not  very  bright,  it  is  very 
hot;,  and  when  we  hold  in  it  a  piece  of  watch-spring,  or  an  old 
penknife-blade,  the  iron  is  burned,  making  a  brilliant  fountain  of 
fire.  The  metal  platinum,  which  does  not  melt  at  the  highest 
furnace  heat,  melts  readily  in  the  oxyhydrogen  flame. 

31.  Fire  is  the  combustion  with  incandescence — that  is,  pro- 
duction of  light  and  heat  at  the  same  time — of  a  solid  substance : 

3* 


30  LESSONS    IN    CHEMISTRY. 

we  have  seen  such  phenomena  in  the  combustion  of  charcoal  and 
iron.  The  oxidation  takes  place  only  on  the  surface  of  the  burn- 
ing body. 

32.  Flame  is  the  combustion  with  incandescence  of  a  gas  or 
vapor,  as  in  the  burning  of  hydrogen,  phosphorus,  and  magne- 
sium :  at  the  borders  of  the  flame  the  gas  or  vapor  may  mix  with 
the  air ;  but  the  interior  of  the  flame  must  consist  of  highly- 
heated,  yet  unburned  gas.  Why  are  certain  flames  very  bright, 
while  others  give  little  or  no  light?  We  burn  a  little  sulphur  in 
a  deflagrating-spoou  in  a  jar  of  oxygen,  and  the  combustion, 
though  very  brilliant,  would  not  serve  for  illumination.  In  order 
to  produce  a  bright  white  light,  a  flame  must  contain  particles  of 
solid  matter  which  may  become  highly  heated.  The  burning 
phosphorus  and  magnesium  were  brilliantly  luminous  because  the 
little  solid  particles  of  phosphoric  oxide  and  magnesium  oxide 
which  were  formed,  became  very  hot.  The  flames  of  hydrogen 
and  sulphur  do  not  give  white  light  because  the  products  of  com- 
bustion, water  in  one  case  and  sulphurous  oxide  in  the  other,  are 
gases  at  the  high  temperature  at  which  they  are  formed,  and 
gases  cannot  be  heated  hot  enough  to  give  white  light.  How- 
ever, the  products  of  combustion  of  tallow,  wax,  and  illuminating 
gas  are  not  solid,  yet  these  substances  are  useful  for  artificial  light. 
In  these  cases  the  illumination  is  due  to  little  particles  of  carbon. 
The  combustible  gases  and  vapors  come  in  contact  with  enough 
oxygen  to  completely  burn  them  only  on  the  outer  edge  of  the 
flame ;  but  the  heat  is  radiated  into  the  flame  as  well  as  from  it, 
and  the  gases,  which  are  compounds  of  hydrogen  and  carbon,  are 
decomposed ;  little  solid  particles  of  carbon  are  set  free,  and  these 
become  very  hot  and  give  out  light :  when  they  reach  the  outside 
of  the  flame  they  are  entirely  consumed,  unless  there  be  too  little 
oxygen,  and  in  that  case  the  flame  smokes.  When  a  cold  body — 
a  piece  of  glass  will  answer — is  held  for  a  moment  in  the  brightest 
part  of  a  lamp-  or  gas- flame,  the  little  particles  of  carbon  are  de- 
posited on  the  cold  surface  in  the  form  of  soot. 

We  may  by  a  very  simple  means  render  the  colorless  flame  of 
hydrogen  quite  brilliant :  we  have  fitted  to  a  bottle  a  cork  through 


OXYGEN. — COMBUSTION. 


31 


which  pass  two  tubes,  the  outer  ends  being  drawn  out  to  fine  jets. 
One  of  these  tubes  is  short,  and  passes  only  through  the  cork ; 
the  other  passes  to  the  bottom  of  the  bottle,  in  which  we  have 
placed  some  broken  pumice-stone  saturated  with  benzine  (Fig.  25). 
To  this  same  tube  is  joined  a  short  side-tube,  which 
ve  connect  with  a  bottle  containing  zinc  and  dilute 
salphuric  acid.  When  all  of  the  air  is  expelled 
f  -oni  the  bottle,  we  light  the  hydrogen  at  the  two 
j  its.  At  one  it  burns  with  a  colorless  flame :  it  is 
t  tie  flame  of  hydrogen  just  as  it  comes  from  the  gen- 
(  rating  bottle.  The  other  flame  is  quite  bright ;  the 
hydrogen  which  has  passed  through  the  benzine  has 
become  charged  with  the  vapor  of  that  volatile  liquid, 
;  nd  as  that  vapor,  containing  hydrogen  and  carbon, 

Is  decomposed  by  the  heat  before  it  burns,  the  carbon  particles 

iccome  incandescent. 
When  the  flame  of  illuminating  gas  or  of  a  lamp  is  supplied 

vith  oxygen  at  the  inside,  the  particles  of  carbon  are  burned  in- 

tantly  and  do  not  become  hot :  the  flame  then  gives  no  light. 
This  is  the  case  in  the  Bunsen   burner  (Fig.  26),  in  which  the 

brce  of  the  escaping  gas  draws  air  through 

aoles  in  a  tube  surrounding  the  jet ;  the  air 

md  gas  mix  together,  and  all  of  the  carbon  is 

•consumed  before  it  can  become  incandescent. 

We  then  have  a  flame  which  gives  great  heat, 

but  docs   not  deposit  smoke  on  any  vessels 

which  we  may  heat  in  it. 

If  we  hold  a  piece  of  lime  in  the  flame  of 

the  oxyhydrogen  blow-pipe,  it  becomes  very 

hot  and  emits  a  brilliant  light.     This  consti- 
tutes the  calcium  or  oxyhydrogen  light  which 

is  used  in  theatres.     Lime  is  used  because  it 

is  neither  burned,  melted,  nor  changed  into 

vapor  by  the  intense  heat. 

33.  Slow    Combustion. — All   of  the    examples    of  oxidation 

which  we  have  so  far  considered  are  said  to  be  cases  of  rapid  com- 


32  LESSONS   IN    CHEMISTRY. 

bustion :  they  take  place  with  the  production  of  intense  heat  and 
light.  Sometimes,  however,  there  is  no  bright  light,  no  high 
temperature,  and  yet  combustion  takes  place  as  certainly  as  before. 
A  piece  of  iron  which  rusts  by  exposure  to  damp  air  is  only  com- 
bining with  oxygen,  and  the  rust  is  a  compound  of  iron  with  the 
oxygen  and  moisture  of  the  atmosphere :  here  the  heat  of  chemi- 
cal union  is  developed  so  slowly  that  it  is  conducted  away  by  the 
air  and  surrounding  bodies,  and  the  iron  does  not  become  heated. 
Respiration  is  a  slow  combustion.  The  warmth  of  our  bodies, 
and  all  our  animal  motions,  are  due  to  the  gradual  oxidation  of  the 
carbon  and  hydrogen  of  our  tissues.  At  every  breath  fresh  oxy- 
gen is  introduced  into  the  lungs,  where  it  is  absorbed  by  the  blood 
and  carried  through  the  arteries  to  the  most  remote  parts  of  the 
system  ;  then,  when  all  of  the  oxygen  in  the  blood  is  used  up,  the 
water  and  carbon  dioxide  produced  by  the  combustion  are  carried 
through  the  veins  to  the  lungs,  and  thrown  out  with  the  exhaled 
air.  Animal  life  itself  depends  on  this  slow  oxidation  :  we  all 
know  how  quickly  any  animal  perishes  from  suffocation  when  the 
supply  of  air  is  entirely  cut  off.  The  muscles  of  our  bodies  con- 
tain no  force  except  that  which  is  produced  by  the  combustion  of 
their  own  substance.  Great  muscular  exertion  consequently  re- 
quires increased  oxidation,  and  we  quickly  become  fatigued  when 
we  are  obliged  to  burn  up  our  tissues  more  rapidly  than  they  are 
remade  from  our  food.  Also,  the  quantity  and  kind  of  food  re- 
quired depend  upon  the  amount  and  kind  of  work  which  we 
must  perform. 


LESSON    IV. 

COMPOSITION   OF    WATER.— CHEMICAL  LAWS    AND 
THEORIES. 

34.  Water  is  the  sole  product  of  the  combustion  of  hydrogen 
in  air  or  oxygen.  Its  composition,  that  is,  the  proportion  in 
which  the  hydrogen  and  oxygen  are  combined  together,  may  be 


COMPOSITION    OF    WATER. 


33 


determined  by  analysis  and  by  synthesis.  Analysis  is  the  separa- 
tion and  weighing  of  the  constituents  of  a  compound;  synthesis 
menus  the  formation  of  a  substance  by  causing  its  elements  to 
unite  in  the  proper  proportion. 

.')5.  Electrolysis  of  Water. — Electrolysis  means  the  decom- 
po>ition  of  a  substance  by  an  electric  current.  For  the  decomposi- 
tio  i  of  pure  water  an  enormously  strong  current  would  be  re- 
qu  red,  and  because  we  do  not  desire  to  use  such  a  strong  current 
we  employ  dilute  sulphuric  acid :  the  final  result  is  the  same  as  if 
we  were  to  use  water,  the  sulphuric  acid  being  found  unchanged 
aft  ;;r  the  experiment.  Instead  of  using  the  acid,  we  might  make 
a  strong  solution  of  ordinary  salt;  the  salt  would  make  the  water 
a  >etter  conductor  of  electricity.  We  introduce  the  dilute  sul- 
pl  uric  acid  (about  five  parts  of  water  to  one  of  acid)  into  a  vessel 
th  'ough  a  hole  in  the  bottom  of  which  are  cemented  two  wires, 
th  j  inner  ends  of  each  being  soldered  to  a  little  plate  of  thin  plat- 
in  im.  We  fill  two  small  test-tubes  with  water,  and,  closing  the 
m  >uths  with  the  fingers,  invert  one  over  each  of  these  plates  :  we 
nc  w  connect  the  ends  of  the  wires  with  the  poles  of  a  voltaic  bat- 
te  y  (Fig.  27).  Little  bubbles  of  gas  at  once  begin  to  rise  in  the 
tubes,  and  as  soon  as 
the  quantities  of  gas  col- 
lected are  large  enough 
to  allow  us  to  notice  the 
volume  of  each,  we  see 
that  in  one  of  the  tubes 
there  is  twice  as  much 
as  in  the  other.  When 
that  tube  is  filled,  we 
raise  it  carefully,  and  jj|^|i 
the  introduction  of  a 
lighted  match  will  con- 
vince us  that  the  gas  is 
hydrogen.  When  we  raise  the  other  tube,  keeping  the  end  closed 
with  the  thumb,  until  we  are  ready  to  push  into  it  a  match-stick 
bearing  a  spark,  the  kindling  of  the  spark  into  flame  shows  us 


FIG.  27. 


34 


LESSONS    IN    CHEMISTRY. 


that  the  second  gas  is  oxygen.     Water  is  then  composed  of  two 

volumes  of  hydrogen  combined  with  one  volume  of  oxygen. 
36.  We  have  seen  that  the  density  of  hydrogen  compared  to 

air  is  0.0693,  and  that  the  density  of  oxygen  is  1.1056.    A  given 

volume  of  oxygen  must  then  be 

1.1056  -r-  0.0693  =  16  (a  very  little  less), 

sixteen  times  as  heavy  as  an  equal  volume  of  hydrogen.  As  we 
have  two  volumes  of  hydrogen  and  only  one  of  oxygen, 
the  oxygen  in  water  must  weigh  eight  times  as  much  as 
the  hydrogen. 

37.  Eudiometric  Synthesis  of  Water. — A  eudio- 
meter is  a  graduated  strong  glass  tube,  closed  at  one  end 
near  which  two  thin  platinum  wires  are  soldered  into 
the  glass  on  opposite  sides ;  an  electric  spark  may  be 
passed  between  the  wires  on  the  inside  of  the  tube 
(Fig.  28).  If  we  fill  such  a  tube  with  mercury,  and, 
after  inverting  it  in  a  vessel  of  mercury,  pass  into  it 
some  hydrogen,  and  .then  half  as  much  oxygen,  an 
electric  spark  will  cause  the  gases  to  combine ;  after  the 
little  explosion  which  takes  place  in  the  tube,  the  water 
which  is  formed  is  condensed  in  minute  drops  in  the 
cold  tube,  and  the  atmospheric  pressure  forces  the  mer- 
cury up,  filling  the  tube  completely.  Here,  again,  we 
see  that  water  is  composed  of  two  volumes  of  hydrogen 
combined  with  one  volume  of  oxygen. 


FIG.  28  FIG.  29. 

38.  Synthesis  by  Weight. — We  may  make  the  synthesis  of 


CHEMICAL    LAWS    AND    THEORIES.  35 

wator  by  a  very  instructive  method  which  was  first  adopted  by  the 
French  chemist  Dumas.  We  prepare  hydrogen  from  sulphuric  acid 
and  zinc  in  the  ordinary  manner,  and  thoroughly  dry  it  by  passage 
through  a  tube  (A)  containing  little  pieces  of  pumice-stone  wet 
witii  strong  sulphuric  acid  (Fig.  29).  We  then  cause  it  to  pass 
through  a  tube  containing  some  cupric  oxide  (B),  a  black  com- 
pound of  copper  and  oxygen,  and  this  tube  is  connected  with  a 
U-shaped  tube  (C)  filled  with  pumice-stone  also  moistened  with 
str<  ng  sulphuric  acid.  The  U  tube  is  placed  in  a  vessel  contain- 
ing some  broken  ice.  Before  connecting  our  tubes  together,  we 
ha^  e  carefully  weighed  that  holding  the  cupric  oxide,  and  the  last 
U  ube  with  its  contents.  When  this  whole  apparatus  is  filled 
wit  si  the  hydrogen  coming  from  the  bottle,  we  heat  the  cupric 
oxi.le  by  a  spirit-lamp,  and  when  it  becomes  hot  the  hydrogen  gas 
tak  as  away  the  oxygen  from  the  copper.  Steam  is  formed  and  is 
coi  densed  in  the  U  tube  (C).  When  the  color  of  the  cupric  oxide 
hat-  entirely  changed  to  red,  we  warm  the  whole  length  of  the 
tul  e  containing  it,  in  order  to  drive  all  of  the  water  over  into  the 
U  ube :  we  allow  our  apparatus  to  cool,  take  it  apart,  and  again 
we:gh  the  tubes  of  which  we  had  determined  the  weight  before 
the  experiment.  The  copper  which  is  left  in  the  first  will  weigh 
just  as  much  less  than  the  cupric  oxide  as  the  latter  has  lost  oxy- 
ger.  The  increased  weight  of  the  U  tube  (C)  will  be  the  weight 
of  the  water  formed,  and  by  subtracting  from  this  weight  the 
weight  of  the  oxygen,  we  will  have  the  weight  of  the  hydrogen 
contained  in  that  water.  '  We  find  that  there  is  almost  exactly 
eight  times  as  much  oxygen  as  hydrogen.  In  very  elaborate  ex- 
periments we  would  perfectly  purify  our  hydrogen  and  adopt  all 
possible  precautions  that  no  vapor  of  water  might  escape  from  the 
tube  C. 

CHEMICAL    LAWS   AND   THEORIES. 

39.  No  matter  by  what  process  water  maybe  formed,  no  matter 

by  what  process  its  composition  may  be  determined,  it  is  always 

found  to  contain  the  same  proportions  of  oxygen  and  hydrogen  ; 

never  more  nor  less  than  eight  (7.98  exactly)  parts  of  the  first 


36 


LESSONS    IN    CHEMISTRY. 


for  one  of  the  second.  If  we  try  to  combine  the  gases  in  other 
proportions,  the  excess  of  the  one  or  other,  out  of  the  proportion 
one  to  eight,  will  be  left  uncoinbined.  The  analysis  of  all  known 
substances  has  shown  a  similar  constancy  of  composition,  a  con- 
stancy which  is  expressed  in  the  following 

40.  LAW  OF   DEFINITE   PROPORTIONS:    The   proportion   in 
which  the  elements  exist  in  any  compound,  is  invariable.     This  is 
generally  called  Dalton's  first  law. 

41.  We  have  already  found  that  the  proportions  by  volume 
according  to  which  oxygen  and  hydrogen  unite  are  one  to  two. 
This  is  a  simple  relation  of  volumes.     Experiments  with  other 
gases  will  in  time   show  us  that  when   gases  combine,  there  is 
always  some  such  simple  relation  between  the  volumes  of  the  gases 
that  enter  into  combination.     Thus, 

One  volume  of  hydrogen  combines  with  exactly  one  volume  of  chlorine. 
Two  volumes  of  hydrogen  combine  with  exactly  one  volume  of  oxygen. 
Three  volumes  of  hydrogen  combine  with  exactly  one  volume  of  nitrogen. 
Two  volumes  of  nitrogen  combine  with  exactly  one  volume  of  oxygen. 

We  might  find  many  more  such  examples,  and  the  statement 
of  these  facts  constitutes 

GAY-LUSSAC'S  FIRST  LAW  :  there  is  a  simple  relation  between 
the  volumes  of  gases  which  combine. 

42.  Let  us  study  the  volume  of  the  compound 
formed  when  that  compound  is  in  the  same  con- 
dition as  the  original  elements  ;  that  is,  the  gaseous 
state. 

By  grinding  together  with  emery,  we  have 
accurately  fitted  together  the  necks  of  two  glass 
bottles  that  have  exactly  the  same  capacity  (Fig. 
30).  We  fill  the  lower  one  with  perfectly  dry 
chlorine  gas  (§  71),  and  the  upper  with  dry  hydro- 
gen, and  then  hermetically  join  them  together  by 
the  ground  joint.  All  of  this  must  be  done  in  a 
room  lighted  only  by  a  candle  or  small  gas-flame. 
We  now*  allow  the  apparatus  to  stand  for  a  day  in 
a  room  where  the  sunlight  may  not  shine  on  it 


FIG.  30. 


COMPOSITION    OF    WATER. 


37 


directly.  The  gases  will  slowly  combine,  and  the  yellowish  color  of 
the  chlorine  will  disappear.  When  we  open  the  bottles  under  the 
sui  face  of  mercury,  we  will  find  that  no  gas  escapes  from  them,  and 
no  mercury  enters.  The  gas  hydrochloric  acid  has  been  formed,  and 

one  volume  of  hydr°Sen  and 
one  volume  of  chlorine. 


Tw  .  volumes  of  hydrochloric  acid  must  contain 


Over  the  open  end  of  a  eudiometer  we  have  passed  a  piece  of 
stiong  rubber  tubing,  to  the  other  end  of  which  is  attached  a 
sti  aight  glass  tube  about  the  size  and  length  of  the  eudiometer  ; 
th  j  rubber  tube  is  firmly  tied  at  each  joint.  We  fill  our  apparatus 
\vi:h  mercury,  place  it  vertically  in  the  mer- 
cury trough,  and  introduce  five  cubic  centi- 
m  'tres  of  oxygen  and  ten  cubic  centimetres 
of  hydrogen.  We  now  close  the  end  of  the 
tu  )e  with  the  finger,  lift  it  from  the  trough, 
ai  L!,  after  bringing  the  two  tubes  parallel  to 
en  ;h  other,  clamp  them  in  that  position  in  a 
st  nd  (Fig.  31).  We  have  tightly  fitted  a 
pc  rforated  cork  around  the  lower  end  of  the 
eudiometer,  and  on  this  cork  we  now  as  tightly 
fit  the  lower  end  of  a  wide  glass  tube,  which 
w<:  slip  over  the  eudiometer,  whose  wires  we 
h;  ve  connected  with  long  copper  wires  that 
pass  out  at  the  upper  end  of  the  wide  tube. 
"We  now  fill  the  wide  tube  with  perfectly  clear 
oi:  (lard  oil  or  sweet  oil)  heated  to  130°  ;  we 
adjust  the  mercury  at  the  same  level  in  the 
two  tubes,  and,  after  carefully  reading  the  vol- 
ume occupied  by  the  mixed  gases,  we  pass  an  electric  spark  in  the 
eudiometer.  The  gases  of  course  combine  :  steam  is  formed,  but 
does  not  condense,  because  the  eudiometer  is  heated.  On  again 
making  the  mercury  levels  the  same,  and  examining  the  volume 
of  this  steam,  we  find  that  it  is  only  two-thirds  as  great  as  that 
of  the  mixed  gases  :  in  other  words, 

m  „   ,  .   .     f  two  volumes  of  hydrogen  and 

Two  volumes  of  steam  contain  ] 

(  one  volume  of  oxygen. 

4 


FIG.  31. 


38  LESSONS   IN    CHEMISTRY. 

Ammonia  gas  is  a  compound  of  hydrogen  and  nitrogen,  and  its 
analysis  proves  that  two  volumes  of  the  gas  may  be  decomposed 
into  one  volume  of  nitrogen  and  three  volumes  of  hydrogen. 

On  comparing  these  results,  we  find  that 

Two  volumes  of  hydrochloric  acid  contain  one  volume  of  hydrogen  and  one 
volume  of  chlorine. 

Two  volumes  of  vapor  of  water  contain  two  volumes  of  hydrogen  and  one  vol- 
ume of  oxygen. 

Two  volumes  of  ammonia  contain  three  volumes  of  hydrogen  and  one  volume 
of  nitrogen. 

We  see  that  not  only  is  there  a  simple  relation  between  the 
volumes  of  gases  which  combine,  but,  as  is  expressed  in 

GAY-LUSSAC'S  SECOND  LAW,  there  is  a  simple  relation  between 
the  volume  of  a  compound  gas  and  the  sum  of  the  volumes  of  the 
gases  which  form  that  compound. 


LESSON    V. 
CHEMICAL  LAWS   AND   THEORIES    (Continued). 

43.  Equivalent  Combining  Proportions. — Careful  analysis 
of  hydrochloric  acid  has  shown  that  it  is  composed  of  35.5  parts 
by  weight  of  chlorine  combined  with  one  part  by  weight  of  hydro- 
gen. Chlorine  combines  with  mercury,  forming  a  compound 
called  mercuric  chloride  or  corrosive  sublimate;  this  compound 
contains  for  every  35.5  parts  of  chlorine,  exactly  100  parts  of 
mercury.  We  dissolve  135.5  grammes  of  mercuric  chloride  in 
water,  and  put  some  zinc  into  the  solution :  the  chlorine  has  a 
stronger  affinity  for  the  zinc  than  for  the  mercury ;  it  conse- 
quently combines  with  the  zinc,  forming  zinc  chloride,  which  re- 
mains in  the  solution,  while  mercury  separates.  If  we  wait  until 
all  of  the  35.5  grammes  of  chlorine  which  were  combined  with 
100  grammes  of  mercury  have  united  with  the  zinc,  and  then  deter- 
mine the  quantity  of  zinc  which  is  required  to  combine  with  that 
quantity  of  chlorine,  we  would  find  that  the  zinc  chloride  formed 


CHEMICAL   LAWS   AND   THEORIES.  39 

weighs  68.25  grammes :  that  is,  32.75  (68.25  —  35.5)  grammes 
of  iinc  combine  with  35.5  grammes  of  chlorine.  Consequently,  as 
far  as  combining  with  chlorine  is  concerned,  32.75  parts  of  zinc 
have  just  as  much  power  as  100  parts  of  mercury. 

Oxygen  combines  with  mercury  and  with  hydrogen :  it  com- 
bii  es  also  with  zinc  and  with  chlorine.  Analysis  of  the  com- 
pounds so  formed  shows  that  35.5  parts  of  chlorine  will  combine 
wi  h  8  parts  of  oxygen,  and  that  8  parts  of  oxygen  will  combine 
wih  32.75  parts  of  zinc  or  with  100  of  mercury.  We  have 
aheady  seen  (§  36)  that  8  parts  of  oxygen  combine  with  one  part 
of  hydrogen.  These  numbers  must  then  express  the  relations 
between  the  combining  quantities  of  the  corresponding  elements. 
Tl  ousands  of  analyses  have  shown  that  similar  equivalent  propor- 
tions exist  for  all  of  the  elements.  The  combining  proportions  so 
fb'ind  must  bear  simple  relations  to  the  relative  weights  of  the 
at  >ms  ;  for  if  atoms  have  a  real  existence,  chemical  combination 
m  ist  result  from  the  union  of  one,  two,  or  more  atoms  of  one 
el  ment  with  one,  two,  or  more  atoms  of  another ;  and,  since 
combination  is  in  definite  proportions,  the  same  substance  must 
always  result  from  the  union  of  the  same  kind  of  atoms  in  the 
sa  ne  proportion. 

44.  If  it  be  possible  to  determine  the  relative  weights  of  the 
molecules,  compared  with  any  unit,  and  to  arrive  at  definite  con- 
clusions as  to  the  number  of  atoms  these  molecules  contain,  then 
wi!  can  determine  the  relative  weights  of  the  atoms.     Some  new 
considerations  will  enable  us  to  make  such  determinations. 

LAW  OF  AVOGADRO  AND  AMPERE.— ATOMIC  THEORY. 

45,  Different  solid  and  liquid  substances  expand  in  very  dif- 
ferent degrees  by  the  action  of  the  same   temperature.     Gases, 
however,  all  expand  alike.     If  at  the  same  pressure  we  raise  or 
lower  the  temperature  of  equal  volumes  of  different  gases  through 
the  same  number  of  degrees,  we  find  that  they  all  expand  or  con- 
tract precisely  the  same  proportion  of  the  volume.     If  expansion 
bo  separation  of  molecules  from  one  another  (§  8),  it  follows  that 
tqual  volumes  of  gases,  measured  at  the  same  temperature  and 


40  LESSONS    IN    CHEMISTRY. 

pressure^  contain  the  same  number  of  molecules.  This  hypothesis, 
proposed  by  Avogadro  and  Ampere,  is  true  if  there  be  such  things 
as  molecules,  and  if  there  be  no  molecules  we  can  explain  no 
chemical  phenomena. 

46.  If  equal  volumes  of  gases  contain  the  same  number  of 
molecules,  the  relative  weights  of  those  equal  volumes  must  also 
express  the  relative  weights  of  the  molecules.  The  relative  weights 
are  the  densities,  and  these  densities  are  usually  calculated  to  ex- 
press the  relation  between  the  weight  of  the  gas  and  that  of  an 
equal  volume  of  air,  which  is  taken  as  unity.     Since  hydrogen  is 
the  lightest  gas,  its  molecule   must  have  the  least  weight :    the 
density  of  oxygen  is  sixteen  times  as  great  as  that  of  hydrogen,  and 
the  molecule  of  oxygen  must  be  sixteen  times  as  heavy  as  that  of 
hydrogen.     Because  of  the  lightness  of  the  molecule  of  hydrogen, 
chemists  have  chosen  that  molecule  as  the  standard  of  comparison 
far  other  molecules,  and  consequently  the  unit  of  density.     The 
density   of  hydrogen   compared   to   air  being  0.0693,  the  air  is 
14.44  times  as  heavy  as  hydrogen  :  consequently  if  we  know  the 
density  of  a   gas  compared   to  air,  we  may  easily  calculate  its 
density  compared  to  hydrogen  by  multiplying  the  first  by  14.44. 
Thus,  the  density  of  vapor  of  water  compared  to  air  is  0.622,  com- 
pared to  hydrogen  it  is  0.622  X  14.44  =  9.     The  molecule  of 
water  (steam)  must  then  be  nine  times  as  heavy  as  that  of  hydrogen. 

47.  Let  us  see  whether  we  can  determine  the  relations  between 
the  weight  of  any  atom  and  that  of  a  molecule  of  hydrogen  ;  and 
for  this  we  must  refer  to  the  experiments  which  led  us  to  Gay- 
Lussac's  laws  (§  42).     According  to  the  law  of  Avogadro  and 
Ampere,  the  molecule  of  oxygen  is  sixteen  times  as  heavy  as  that 
of  hydrogen.     Hydrogen  combines  with  only  half  its  volume  of 
oxygen,  and  if  water  consist  of  one  atom  of  hydrogen  combined 
with    one    atom    of  oxygen,   the    last    must  be   eight  times    as 
heavy  as  the  first  :  this  would  make  the  molecule  of  water  nine 
times  as  heavy  as  the  atom   (or  molecule)  of  hydrogen.     But 
hydrogen  and   chlorine  combine  in  equal  volumes,  and  no  con- 
traction  results  from  the  combination   (§  41).      Since  the  chlo- 
rine is  35.5  times  as  heavy  as  the  hydrogen,  the  molecular  weight 


CHEMICAL    LAWS    AND    THEORIES.  41 

of  the  compound,  or  its  density  referred  to  hydrogen,  is  £  (35.5 
-|-  1)  =  18.25.  But  this  molecule  would  contain  only  half 
as  much  hydrogen  as  combined  with  the  oxygen  to  form  a 
molecule  of  water ;  we  supposed  the  hydrogen  in  a  molecule  of 
wa  ;er  to  be  only  one  atom,  and  atoms  are  indivisible.  Therefore 
we  must  conclude  that  the  two  volumes  of  hydrogen  which  com- 
bii  e  with  one  volume  of  oxygen  represent  two  atoms>  and  the 
att  m  of  oxygen  is  then  sixteen  times  as  heavy  as  that  of  hydrogen. 

i8.  Now  we  may  apply  our  theory  to  the  facts  already  studied. 

Two  volumes  of  hydrogen  represent  two  atoms,  each  of  which 
weighs  one  :  two  volumes  of  oxygen  represent  two  atoms,  each  of 
wl  ich  weighs  sixteen.  Water  is  formed  by  the  union  of  two 
at<  ms  of  hydrogen  and  one  atom  of  oxygen,  and  a  molecule  of 
w;  ter  weighs  eighteen  times  as  much  as  an  atom  of  hydrogen. 

A  molecule  of  hydrochloric  acid  contains  one  atom  of  hydrogen 
ai)  .1  one  atom  of  chlorine,  and  this  molecule  weighs  36.5  if  one 
at  >m  of  hydrogen  weighs  1. 

A  molecule  of  ammonia  contains  one  atom  of  nitrogen  (weigh- 
in  c  14)  and  three  atoms  of  hydrogen,  and  is  17  times  as  heavy  as 
an  atom  of  hydrogen. 

But  the  density  of  water  compared  to  hydrogen  is  9 ;  that  of 
hydrochloric  acid,  18.25,  and  that  of  ammonia,  8.5.  We  see  then 
th  it  if  an  atom  of  hydrogen  occupies  one  volume  and  weighs  one, 
tho  molecule  of  any  gas  or  vapor  must  occupy  twice  as  much  vol- 
ume as  one  atom  of  hydrogen,  and  the  weight  of  the  molecule 
will  be  expressed  by  twice  the  density  referred  to  hydrogen.  We 
must  remember  that  the  molecule  of  hydrogen  contains  two 
atoms,  each  of  which  weighs  1. 

Different  methods  are  employed  for  determining  the  atomic 
weights  of  the  elements.  At  this  point  we  need  only  understand 
that  if  the  element  be  gaseous  or  volatile,  and  if  we  have  reason  to 
believe  that  its  molecule  contains  two  atoms,  then,  since  the  mole- 
cule of  hydrogen  consists  of  two  atoms,  and  equal  volumes  of 
gases  contain  equal  numbers  of  molecules,  the  same  figures  which 
express  the  density  of  the  gas  compared  to  hydrogen,  will  express 
also  the  atomic  weight. 


42  LESSONS    IN    CHEMISTRY. 

This  atomic  theory,  which  has  been  slowly  developed  during  the 
present  century,  furnishes  an  intelligible  explanation  of  chemical 
phenomena.  New  discoveries  are  continually  bringing  new  facts  to 
its  support,  and,  though  it  may  be  modified  by  the  results  of  future 
researches,  its  principal  features  will  probably  remain  undisturbed. 

CHEMICAL  NOTATION. 

49.  In  order  that  the  composition  of  a  substance,  that  is,  the 
number  and  kinds  of  atoms  in  its  molecules,  may  be  understood  at 
a  glance,  we  employ  a  special  method  of  representing  elements  and 
compounds.     The  first  letter,  or  the  first  and  another  letter,  of 
the  name  of  an  element,  .is  used  to  express  one  atom  of  that  ele- 
ment.    Thus,  H  means  one  atom  of  hydrogen  ;  0,  one  of  oxygen  ; 
S,  one  of  sulphur ;  C,  one  of  carbon,  and  Ca,  one  of  calcium. 
These  letters  are  called  the  symb9ls  of  the  elements.     More  than 
one  atom  is  expressed  by  a  little  figure  placed  to  the  right  of 
the  symbol,  slightly  above  or  below  its  central  line ;  H2  (read,  H 
two)  means  two  atoms  of  hydrogen  ;  O4  represents  four  atoms  of 
oxygen.     Compounds  are  then  written  so  that  the  symbols  enter- 
ing into  the  formulae  express  the  number  and  kind  of  atoms  in  a 
molecule.      H20  means  a  molecule  of  water,  composed  of  two 
atoms  of  hydrogen  and  one  of  oxygen  :   H2S04  means  a  molecule 
of  sulphuric  acid,  containing  two  atoms  of  hydrogen,  one  of  sul- 
phur, and  four  of  oxygen.     To  express  any  number  of  molecules 
we  use  an  ordinary  figure  placed  to  the  left  of  the  formula ;  thus, 
2HC1  means  two  molecules  of  hydrochloric  acid,  each  of  which 
contains  one  atom  of  hydrogen  and  one  of  chlorine. 

50.  We  may  now  study  the  molecular  changes  which  have  oc- 
curred in  the  chemical  phenomena  that  we  have  already  observed. 
In  the  decomposition  of  water  by  sodium,  one  atom  of  hydrogen 
in  each  molecule  of  water  is  replaced  by  sodium,  and  when  a  mole- 
cule of  hydrogen  is  set  free,  two  molecules  of  a  compound  called 
sodium  hydrate  are  formed.     We  represent  the  change  thus : 

2H20  +         Na2  2NaOH         +  H2 

2  molecules  of  2  atoms  of  2  molecules  of  1  molecule  of 

water.  sodium.  sodium  hydrate.  hydrogen. 

This  chemical  equation  expresses  the  changes  which  take  place 


CHEMICAL    LAWS    AND    THEORIES.  43 

in  the  chemical  reaction.  As  the  symbol  for  each  atom  means  a 
definite  quantity  of  matter,  and  as  there  can  be  no  change  in  the 
quantity  of  matter  during  the  reaction,  there  must  be  as  many 
at  >ms  represented  in  one  member  of  the  equation  as  in  the  other. 
When  we  know  what  is  formed  by  the  reaction  of  certain  mole- 
cules, our  equation  will  enable  us  to  calculate  the  quantities  of  the 
substances.  The  weight  of  one  atom  of  sodium  being  23;  one 
at  >m  of  hydrogen,  1  ;  and  one  atom  of  oxygen,  16,  we  find  that 
4i!  grammes  of  sodium  will  yield  2  grammes  of  hydrogen,  and  80 
gi  ;immes  of  sodium  hydrate. 

HOH      +      Na*     =          2NaOH        +     H2 
1+16  +  1        23  +  23        2(23  +  16  +  1)         1+1. 

We  can  calculate  the  volume  of  the  hydrogen  at  0°,  from  its 
\v  ;ight  (§  19),  and  we  can  so  estimate  the  quantity  of  hydrogen 
\v  lich  will  be  set  free  by  any  quantity  of  sodium. 

The  action  of  hydrochloric  acid  on  zinc  (§  18)  can  be  expressed 

Zn    +  2HC1  ZnCl2         +        IP 

Zinc.        Hydrochloric  acid.        Zinc  chloride.        Hydrogen. 

The  action  of  sulphuric  acid  on  zinc,  which  yields  zinc  sulphate 
ai  d  hydrogen,  is  written 

Zn  +        H2SO*        -        ZnSO*        +  H2 
Sulphuric  acid.        Zinc  sulphate. 

Of  course  we  must  know  by  experiment  what  is  formed  in  a 
reaction,  before  we  can  write  the  chemical  equation  ;  we  must  also 
know  by  analysis  the  proportions  of  the  elements  in  any  compound 
before  we  can  write  a  formula  which  we  believe  to  express  the 
atoms  in  its  molecule. 

The  decomposition  of  potassium  chlorate  by  heat  (§  26)  is 

2KC103  2KC1  +      302 

Potassium  chlorate,        Potassium  chloride,        Oxygen, 
2  molecules.  2  molecules.  3  molecules. 

Thut  of  mercuric  oxide,  in  the  same  manner,  is 

2HgO  2Hg       +  O2 

Mercuric  oxide.        Mercury. 

The  reaction  of  hydrogen  with  cupric  oxide,  which  enabled  us 
to  make  the  synthesis  of  water,  is  written 

CuO        +  H2  =  H20  +      Cu 

Cupric  oxide.  Copper. 


44 


LESSONS   IN    CHEMISTRY. 


51.  The  following  table  gives  the  names  and  symbols  of  the 
elements  which  are  at  present  known,  and  the  weights  of  the 
atoms  compared  to  the  weight  of  an  atom  of  hydrogen.  Some  of 
these  atomic  weights  might  be  more  exactly  expressed ;  an  atom 
of  oxygen  is  15.96  times  as  heavy  as  that  of  hydrogen  ;  the  exact 
atomic  weight  of  nitrogen  is  14.01  ;  but  these  numbers  are  so 
nearly  16  and  14,  that  for  memory's  sake  it  is  preferable  to  use 
the  nearest  whole  numbers. 


NAMES  OF  THE  ELE- 
MENTS. 

Symbols. 

Atomic 
Weights. 

NAMES  OF  THE  ELE- 
MENTS. 

Symbols. 

Atomic 
Weights. 

Aluminium  .  .  . 
Antimony  (stibium) 
Arsenic  .... 
Barium  .... 
Bismuth  .... 
Boron  .  . 

Al 
Sb 
As 
Ba 
Bi 
Bo 

27.5 
120 
75 
137 
210 
11 

Molybdenum 
•  Nickel  .          ... 
Niobium         .     .     . 
Nitrogen        .     . 
Osmium          .     .     . 
Oxvffen 

Mo 
Ni 
Nb 
N 
Os 
0 

96 
59 
94 
14 
199.2 
16 

Bromine   .... 
Cadmium  .... 
Caesium     .... 
Calcium     .... 
Carbon      .... 
Cerium      .... 
Chlorine    .... 
Chromium 
Cobalt  

Br 

Cd 
Cs 
Ca 
C 
Ce 
Cl 
Cr 
Co 

80 
112 
133 
40 
12 
141.2 
35.5 
52.5 
59 

Palladium      .     .     . 
Phosphorus    .     .     . 
Platinum  .... 
Potassium  (kalium) 
Rhodium  .... 
Rubidium      .     .     . 
Ruthenium    .     .     . 
Samarium      .     . 
Scandium 

Pd 
P 
Pt 
K 

Rh 
Rb 
Ru 

Sa 
Sc 

106.6 
31 
197.5 
39.1 
104.4 
85.2 
104.4 
150 
44 

Copper      .... 
Didymium     .     .     . 
Erbium     .... 
Fluorine  ".     .     .     . 
Gallium     .... 
Glucinum  .... 
Gold  (aurum)     .     . 
Holmium  .... 
Hydrogen      .     . 
Indium     .... 
Iodine  .... 

Cu 
Di 
Er 
Fl 
Ga 
Gl 
Au 
Ho 
H 
In 
I 

63.5 
145.4 
166 
19 
69. 
9.5 
197 
162  (?) 

113.4 
127 

Selenium  .... 
Silicon       .... 
Silver  (argentum)  . 
Sodium  (natrium)  . 
Strontium      .     . 
Sulphur     .... 
Tantalum  .... 
Tellurium 
Thallium  .... 
Thorium    .... 
Tin  (stannum)  . 

Se 

Si 

4g 
Na 

Sr 
S 
Ta 
Te 
Tl 
Th 
Sn 

79.5 
28 
108 
23 
87.5 
32 
182 
128 
204 
234 
118 

Iridium     .... 
Iron  (ferrum)     .     . 
Lanthanum   . 
Lead  (plumbum)     . 
Lithium    .... 
Magnesium    . 
Manganese    . 
Mercury     (hydrar- 

Ir 

Fe 
La 
Ph 
Li 
Mg 
Mn 

198 
56 
139 
207 
7 
24 
55 

Titanium  .... 
Thulium    .... 
Tungsten     (wolfra- 
mium)  .... 
Uranium  .... 
Vanadium     .     .     . 
Yttrium     .... 
Zinc      

Ti 
Tu 

W 
Ur 

V 
Y 
Zn 

50 
170.4(?) 

184 
120 
51.37 
172.5 
65.2 

gyrum)       .     .     . 

Hg 

200 

Zirconium  .  .  . 

Zr 

90 

PROPERTIES   OF   WATER.  45 


LESSON    VI. 

PROPERTIES    OF  WATER.— POTABLE   AND   MINERAL 
WATERS. 

52.  Pure  water  is.  not  met  with  in  nature.  When  we  desire  it, 
it  must  be  prepared  by  distilling  water ;  that  is,  boiling  it  in  a  re- 
to  t,  and  condensing  the  steam.  We  usually  conduct  this  distilla- 
te n  in  tin-lined  copper  retorts.  For  most  of  the  distillations  in 
th  3  laboratory  we  employ  a  flask  or  retort,  connected  with  a  long 
tuoe  which  is  surrounded  by  a  wider  tube,  and  a  stream  of  cold 


FIG.  32. 

water  continually  flows  through  the  space  between  the  two  tubes 
in  this  condenser,  as  we  call  it  (Fig.  32). 

Pure  water  has  neither  taste  nor  odor ;  although  it  is  colorless 
in  small  quantity,  it  has  a  deep-blue  color  when  in  large  masses. 
It  solidifies  when  sufficiently  cooled,  and,  since  it  is  always  con- 
verted into  ice  at  the  same  temperature,  that  temperature  is  taken 
as  0°  in  the  centigrade  thermometer  scale  which  we  use  in  the 
laboratory. 

53.  The  temperature  of  water  does  not  change  while  it  is  freez- 
ing, and  that  of  ice  does  not  change  while  it  is  melting.  This  is 
because  all  of  the  heat  which  is  communicated  to  ice  during  its 
melting  is  required  to  produce  the  change  of  state  ;  indeed,  one 


46  LESSONS    IN   CHEMISTRY. 

kilogramme  of  ice  at  0°  requires  as  much  heat  to  melt  it  as  would 
raise  79  kilogrammes  of  water  from  0°  to  1°,  or  one  kilogramme 
from  0°  to  79°,  and  yet  the  water  from  the  melted  ice  still  has  a 
temperature  of  0°.  Ice  is  crystallized ;  it  consists  of  a  great  many 
little  six-sided  pyramids  dovetailed  together.  We  can  notice  the 


FIG.  33. 

crystalline  form  of  water  by  examining  some  snow-flakes  that  have 
fallen  on  black  cloth  (Fig.  33). 

During  the  cooling  of  water,  it  contracts  in  volume  until  its 
temperature  reaches  4°  ;  it  then  begins  to  expand,  and  on  freezing 
expands  considerably.  Ice  is  only  0.93  as  heavy  as  water  at  4°. 
Strong  vessels  are  broken  by  the  freezing  of  water  in  them,  and 
it  is  the  same  expansion  which  kills  delicate  plants  by  frost,  for 
the  ice  formed  in  them  tears  apart  the  fibres  and  destroys  the  sap- 
vessels.  Since  it  is  easy  everywhere  to  obtain  water  at  its  point 
of  maximum  density,  that  is,  4°,  this  density  has  been  chosen  as 
the  unit  of  density  or  specific  gravity  for  liquids  and  solids.  It 
is  also  at  this  temperature  that  one  litre  of  water  weighs  one  kilo- 
gramme. 

Water  and  ice  continually  emit  invisible  vapor,  but  water  does 
not  begin  to  boil  until  its  tension  of  vapor  *  is  equal  to  the  at- 
mospheric pressure.  We  consider  that  the  normal  atmospheric 
pressure  is  equal  to  760  millimetres  of  mercury,  and  under  this 


*  The  tension  of  vapor  of  a  liquid  at  any  temperature  is  measured  by  the 
decrease  in  the  height  of  the  mercury  in  a  barometer-tube,  up  into  which  the 
liquid  is  passed  in  small  quantities  until  no  more  of  it  changes  into  vapor. 
The  number  of  millimetres  through  which  the  level  of  the  mercury  has  then 
fallen,  expresses  the  tension  of  the  vapor. 


PROPERTIES    OF    WATER.  47 

pressure  the  boiling  point  of  water  is  selected  as  the  100°  point 
in  the  centigrade  thermometric  scale  which  we  use. 

While  water  is  boiling,  its  temperature  does  not  rise  :  after  it 
has  reached  the  boiling  point,  all  the  heat  passes  into  the  steam, 
whc  re  it  is  required  to  hold  apart  the  molecules.  To  convert  one 
kilogramme  of  water  at  100°  into  steam  requires  enough  heat  to 
rais  3  the  temperature  of  537  kilogrammes  of  water  from  0°  to  1°, 
or  .''.37  kilogrammes  from  0°  to  100°.  The  conversion  of  water 
int(  steam  expands  it  1696  times :  that  is,  one  litre  of  water  will 
yu>  d  1696  litres  of  steam  at  100°. 

T  4.  Chemical  Properties. — We  have  seen  that  water  is  de- 
cor iposed  by  an  electric  current:  it  is  also  decomposed  by  very 
hi<^i  temperatures  (1200°).  We  will  find  that  it  enters  into 
ma  ly  chemical  reactions,  in  some  of  which  it  is  decomposed  and 
pai  of  its  hydrogen  set  free,  as  in  the  experiment  with  sodium 
(§  >).  In  other  cases  both  the  oxygen  and  hydrogen  atoms  are 
tak  3n  into  new  combinations.  Water  forms  a  large  proportion  of 
ani  nal  and  vegetable  tissues. 

Vater  dissolves  many  substances,  solid,  liquid,  and  gaseous. 
W(  all  know  that  salt,  sugar,  and  alum  will  dissolve  in  water,  be- 
coming for  the  time  part  of  the  liquid.  We  immerse  the  bulb  of 
a  thermometer  in  a  vessel  of  water,  into  which  we  throw  some 
ammonium  nitrate,  and  stir  the  liquid:  at  once  the  thermometer 
indicates  a  lower  temperature.  When  solids  dissolve  in  water, 
cold  is  produced,  because  the  heat  required  to  separate  the  mole- 
cules of  the  solid  must  be  taken  from  the  water.  On  the  con- 
trary, when  gases  dissolve  in  water,  the  liquid  becomes  warmer, 
because  the  heat  no  longer  required  to  hold  apart  the  molecules 
of  the  gas  can  now  raise  the  temperature. 

55.  Water  exerts  a  very  curious  action  on  some  substances. 
Wo  take  some  large  blue  crystals  of  cupric  sulphate  and  heat 
them  on  a  piece  of  tin  over  a  lamp.  We  see  that  they  gradually 
become  white,  and  crumble  into  a  powder.  We  throw  some  of 
this  powder  into  water,  and  the  water  becomes  blue ;  cupric  sul- 
phate can  only  exist  in  crystals  when  it  is  combined  with  water, 
and  it  is  blue  only  when  combined  with  water.  In  the  same 


48  LESSONS    IN   CHEMISTRY. 

manner  water  is  necessary  to  the  crystalline  form,  and  often  to 
the  color,  of  many  substances,  and  when  combined  in  this  way  is 
called  water  of  crystallization.  Water  of  crystallization  is  chem- 
ically combined  in  the  crystals,  for  it  is  always  in  definite  propor- 
tions. In  a  piece  of  crystallized  cupric  sulphate  there  are  five 
molecules  of  water  for  every  molecule  of  copper  sulphate. 

56.  NATURAL  WATER. — As  it  occurs  naturally,  water  always 
contains  foreign  .matters  suspended  or  dissolved  in  it.     These  sub- 
stances are  derived  from  the  air  through  which  the  rain  falls,  or 
from  the  soil  over  which  the  water  flows. 

57.  According  to  the  kind  and  quantity  of  these  matters  pres- 
ent, the  water  is  potable,  mineral,  or  unfit  for  drinking  and  cook- 
ing.     Potable   or   drinking  water   should  be  cool,  limpid,   and 
odorless,  having  a  very  feeble  but  pleasant  taste  that  should  be 
neither  bitter,  salty,  nor  sweet.     It  should  also  make  suds  with 
soap  without  forming  a  curd.     Water  which  possesses  these  prop- 
erties always  holds  in  solution  a  certain  quantity  of  the  gases  of 
the  air,  oxygen,  nitrogen,  and  carbon  dioxide,  and  usually  a  small 
quantity  of  mineral  matters.     The  gases  are  absolutely  essential 
to  good  water,  but  their  quantity  varies  considerably  in  different 
waters,  and  at  different  times  in   water  from   the  same  source. 
This  dissolved  air  separates  from  water  which  stands  in  a  warm 
place,  and  part  of  it  collects  on  the  sides  of  the  vessel  in  small 
bubbles,  which  we  have  all  seen  in  a  glass  of  water  that  has  stood 
for  several  hours.     Fish  cannot  live  in  water  containing  no  dis- 
solved oxygen  ;  they  do  not  breathe,  but  their  gills  remove  the 
dissolved  oxygen   from  the  water  which  they  continually  draw 
through  those  organs  (see  §  33). 

The  solid  matters  in  a  potable  water  should  not  exceed  two  or 
three  decigrammes  per  litre,  and  these  matters  should  be  entirely 
mineral.  They  usually  consist  of  compounds  of  calcium  and  mag- 
nesium ;  magnesium  sulphate  and  calcium  sulphate  being  the 
most  common,  while  a  small  proportion  of  common  salt  is  gener- 
ally present. 

58.  When  larger  quantities  of  calcium  compounds  are  present, 
we  have  no  longer  a  soft  but  a  hard  water.     Hard  waters  contain 


MINERAL    WATERS.  49 

eitiier  calcium  sulphate  or  calcium  carbonate.  Water  dissolves 
ouiy  a  very  small  quantity  of  calcium  sulphate,  but  then  has  a 
peculiar  taste  and  curdles  the  soap  when  we  use  it  for  washing. 
Wo  add  a  few  drops  of  a  solution  of  barium  chloride  to  some 
wa:er  containing  a  little  calcium  sulphate,  and  instantly  a  white 
cloud  appears:  this  is  caused  by  the  formation  of  an  insoluble 
bo  ly  called  barium  sulphate,  and  the  test  makes  us  sure  that  the 
w;  tor  contained  a  sulphate.  Calcium  carbonate  is  insoluble  in 
pure  water,  but  it  dissolves  in  water  containing  carbonic  acid  gas, 
or  carbon  dioxide.  When  such  water  is  boiled,  the  carbon  dioxide 
is  driven  out,  and  then  the  calcium  carbonate  separates,  for  it  is 
no  longer  soluble.  Hence  we  have  a  method  of  curing  hard 
w;  ler  which  contains  only  calcium  carbonate  and  carbonic  acid: 
w<  boil  it,  and  allow  it  to  settle,  and  after  pouring  off  the  clear 
w,  ter  expose  it  to  the  air  for  a  time,  so  that  it  may  dissolve  some 
of  the  gases  from  the  atmosphere. 

59.  Drinking-water  must  not  contain  animal  or  vegetable  sub- 
st  .nces :   they  render  it  very  unwholesome.      Happily,  the  waters 
of  rivers,  which  become  contaminated  with  so  many  such  impuri- 
tit  s,  generally  become   purified  during   their  exposure  to'  the  air, 
because  the  foul  matter  is  gradually  oxidized.     Water  containing 
thase  matters  usually  has  a  sweetish  taste  and  a  disagreeable  odor, 
which  may,  however,  be  very  faint.     It  may  be  purified  by  passing 
it  through  a  charcoal  filter  (§  227). 

60.  MINERAL  WATERS  contain  various  dissolved  mineral  mat- 
te !*s.     Some  are   hot,  others  warm,  and  still  others  cold.     Those 
wiiich  effervesce  or  sparkle   contain  a  considerable  proportion  of 
carbonic  acid  gas  in  solution,  and  it  is  the  escape  of  this  gas  which 
produces  the  sparkling.      Apollinaris  water  contains,  besides  the 
carbonic  acid  gas,  principally  a  little  sodium  acid  carbonate,  com- 
mon salt,  and  magnesium  and  sodium  sulphates.      Buffalo  lithia 
water  contains  very  little  of  the  sodium  compounds,  but  consider- 
able quantities  of  calcium  sulphate,  with  carbonates  of  potassium, 
calcium,  barium,  and  lithium. 

Saratoga  water  has  a  large  proportion  of  calcium  and  magnesium 
carbonates  dissolved  by  the  excess  of  carbon  dioxide  which  it  cou- 
d  5 


50  LESSONS    IN    CHEMISTRY. 

tains,  and  a  very  large  proportion  of  common  salt.  Gettysburg 
water  contains  principally  the  carbonates  of  calcium,  magnesium, 
and  sodium,  together  with  a  little  dissolved  silica :  its  excess  of 
carbon  dioxide  is  quite  small.  Hunyadi  Janos  contains  sulphates 
of  magnesium,  sodium,  calcium,  and  potassium ;  these  substances 
give  to  it  purgative  properties,  in  which  it  is  resembled  by  Fried- 
richshall  water,  for  the  composition  of  the  latter  is  somewhat 
similar. 

Chalybeate  waters  are  such  as  contain  either  iron  carbonate, 
held  in  solution  by  an  excess  of  carbon  dioxide,  or  ferrous  sul- 
phate :  in  the  former  case  the  water  becomes  muddy  on  exposure 
to  the  air,  for  as  the  carbon  dioxide  escapes,  ferrous  carbonate  is 
deposited.  The  Mercer  County  water,  of  Virginia,  contains  a 
large  proportion  of  ferrous  sulphate.  Iron  waters  are  usually 
cold. 

Sulphur  waters  owe  their  odors  and  their  virtues  to  hydrogen 
sulphide  and  sulphides  of  potassium  and  sodium.  They  are  gen- 
erally warm,  or  even  hot. 


LESSON    VII. 

NOMENCLATURE   OP   COMPOUNDS    OP   OXYGEN- 
OZONE.— HYDROGEN  DIOXIDE. 

61.  Besides  being  able  to  express  the  composition  of  molecules 
by  chemical  formulae,  as  we  have  learned,  it  is  important  that  we 
may  have  distinctive  names  for  each  substance,  and  that  those 
names  may  express  as  far  as  possible  the  composition  of  the  mole- 
cules. A  compound  of  only  two  elements  is  called  a  binary  com- 
pound ;  one  containing  three  is  a  ternary  compound ;  one  con- 
taining four,  a  quaternary.  We  may  be  satisfied  at  present  to 
study  a  system  of  naming — a  nomenclature — for  the  binary  com- 
pounds of  oxygen.  These  are  called  oxides. 


NOMENCLATURE    OF    COMPOUNDS    OF   OXYGEN,  ETC.          51 


FlG.  34. 


We  place  a  small  piece  of  phosphorus  on  a  piece  of  glass  on  a 
plate,  light  it,  and  cover  it  with  a  bell-jar  (Fig.  34).  The  phos- 
phorus combines  with  the  oxy- 
gen of  the  air,  and  the  com- 
pound which  is  formed  settles 
like  flakes  of  snow  in  the  jar 
an  1  on  the  plate.  This  is  an 
oxide  of  phosphorus.  On  another 
pi  tte,  in  the  same  manner,  we 
bi-rn  a  small  piece  of  sodium  : 
w<  have  here  formed  sodium 
o>  ide.  Now  we  rinse  out  each 
ja  and  plate  with  a  little  water : 
w  len  the  water  comes  in  con- 
ta  :t  with  the  oxides  that  have 
b»  en  formed,  there  is  a  hissing 
IK  ise,  and  the  jars  become 

w  .rm,  showing  that  energy  has  been  developed  ;  there  is  a  chem- 
ie  il  action  between  the  water  and  the  oxide.  We  pour  into  sepa- 
ra.e  vessels  the  liquids  from  the  two  jars,  and  to  that  from  the 
pi  osphorus  oxide  we  add  some  blue  litmus  solution,  prepared  by 
b<  iling  litmus,  a  substance  made  from  a  peculiar  moss,  with  water. 
T;ie  blue  color  instantly  changes  to  red.  We  pour  some  of  this 
rel  liquid  into  the  water  from  the  sodium  experiment,  and  the 
blue  color  at  once  reappears.  It  is  certain  then  that  our  two 
oxides  have  different  properties,  and  the  study  of  these  and  other 
oxides  has  shown  that  when  oxygen  combines  with  a  non-metal- 
lic, element,  the  resulting  oxide  usually  combines  with  water,  and 
forms  a  substance  which  changes  blue  litmus  to  red.  Such  sub- 
stances generally  have  a  sour  taste,  and  are  called  acids.  On  the 
contrary,  the  oxides  of  the  metallic  elements  usually  change  the 
reddened  litmus  to  blue,  and  are  called  basic  oxides.  Some  oxides, 
however,  have  no  effect  on  either  red  or  blue  litmus. 

62.  When  an  oxide  reacts  with  water,  a  body  called  a  hydrate 
is  formed.  The  acids  containing  oxygen  are  hydrates  correspond- 
ing to  non-metallic  oxides,  while  the  metallic  oxides  usually  have 


52  LESSONS    IN    CHEMISTRY. 

corresponding  metallic  hydrates.  We  have  seen  the  formation  of 
sodium  hydrate  'by  the  action  of  sodium  on  water ;  this  same  com- 
pound results  from  the  action  of  water  on  sodium  oxide,  and  we 
will  notice  that  the  only  difference  between  the  hydrate  and  water 
is  that  the  former  contains  an  atom  of  sodium  in  place  of  one  atom 
of  hydrogen. 

Na20         f     H20    =         NaOH          -f  NaOH 

Sodium  oxide.        Water.        Sodium  hydrate.         Sodium  hydrate. 

63.  An  analysis  of  the  oxide  of  phosphorus  which  we  have 
formed,  shows  that  its  molecule  contains  one  atom  of  phosphorus 
and  five    atoms  of  oxygen ;    it   is    therefore   called  phosphorus 
pentoxide*  and,  because  the  acid  which  it  forms  is  called  phos- 
phoric acid,   the   oxide   is  sometimes    called    phosphoric    oxide. 
In  general,  the  name  of  an  oxygen  compound  is  formed  by  putting 
oxide  after  the  name  of  the  other  element,  and  to  the  word  oxide 
is  prefixed  the  Greek  name  of  the  number  of  atoms  of  oxygen  in  a 
molecule  of  the  oxide. 

A  monoxide  contains  one  atom  of  oxygen,  a  dioxide  contains 
two  atoms  of  oxygen,  a  trioxide  contains  three,  a  tetroxide  con- 
tains four,  a  pentoxide  five. 

The  word  sesquioxide  is  sometimes  used  to  indicate  a  com- 
pound whose  molecule  contains  three  atoms  of  oxygen  and  two 
atoms  of  the  other  element :  sesqui  means  one  and  a  half.  Man- 
ganese sesquioxide  con  tains.  Mn203. 

Sometimes  an  element  forms  more  than  one  compound  with 
oxygen.  Nitrogen  forms  five  ;  and  when  we  have  learned  that  a 
molecule  of  each  of  these  oxides  contains  two  atoms  of  nitrogen, 
the  names  will  at  once  indicate  the  composition  of  the  molecules. 

Nitrogen  monoxide,  N20. 
Nitrogen  dioxide,  N202. 
Nitrogen  trioxide,  N203. 
Nitrogen  tetroxide,  N204. 
Nitrogen  pentoxide,  N205. 

64.  Frequently  when  there  are  only  two  oxides  of  an  element, 
or  when  there  are  two  of  special  importance,  the  word  oxide  is 


Penta — five. 


NOMENCLATURE   OF   COMPOUNDS   OF   OXYGEN,  ETC.          53 

not  changed,  but  the  name  of  the  other  element  is  made  to  end  in 
fc  or  ous.  There  are  only  two  oxides  of  mercury  ;  that  containing 
the  largest  proportion  of  oxygen  is  called  mercuric  oxide,  while 
that  containing  the  least  proportion  is  mercurous  oxide.  Their 
molecules  contain 

Mercuric  oxide,     HgO. 
Mercurous  oxide,  Hg20. 

dach  of  the  two  more  important  oxides  of  sulphur  contains  one 
at<  m  of  sulphur  combined  respectively  with  three  and  two  atoms 

of  oxygen. 

Sulphuric  oxide,     SO3. 
Sulphurous  oxide,  SO'2. 

The  oxide  whose  name  ends  in  ic  then  contains  a  larger  propor- 
tio  i  of  oxygen  than  that  whose  name  ends  in  ous,  and  we  should 
no  use  these  terminations  unless  there  be  two  oxides  of  the 
ek  ment. 

We  can  now  understand  what  is  meant  when  we  say  that  water 
is  lydrogen  oxide,  and  we  will  presently  learn  the  signification  of 
all  the  names  which  we  have  been  obliged  to  use. 

OZONE. 

)5.  Before,  and  sometimes  during,  a  thunder-storm,  there  is 
oft ^n  a  peculiar  odor  in  the  air,  and  the  same  odor  may  be  noticed 
nej  r  a  good  electric  machine  in  operation.  It  has  been  found  that 
the  air  has  at  the  same  time  acquired  more  active  oxidizing  prop- 
ert  es  than  it  had  before.  It  will  even  bleach  many  coloring  mat- 
ters. Part  of  the  oxygen  of  the  atmosphere  has  been 
changed  to  a  body  which  we  call  ozone. 

66.   We  can  produce  this  change  by  a  simple  experi- 
ment.     Under  the  surface  of  some  water  we  scrape  the 
outside  of  a  stick  of  phosphorus,  so  that  it  may  be  per- 
fectly free  from  oxide,  and  then  put  it  into  a  bottle 
containing  enough  water  to  about  half  cover  the  phos- 
phorus,  so  that  it  may  not  take  fire  (Fig.  35).     After 
it   has  stood  for  a  little  while,  we  dip  into  the  air  in  the  bottle  a 
piece  of  paper  that  has  been  soaked  in  some  starch  boiled  in  water 
to  which  a  little  potassium  iodide  has  been  added.     We  see  that 

5* 


54 


LESSONS    IN    CHEMISTRY. 


the  paper  at  once  becomes  blue.  Now  let  us  put  a  drop  of  a  solu- 
tion of  iodine  in  alcohol  on  a  piece  of  paper  soaked  in  starch  to 
which  no  potassium  iodide  was  added.  The  same  blue  color 
appears.  Potassium  iodide  is  a  compound  of  potassium  and  iodine, 
and  the  blue  color  is  due  to  the  action  of  ozone,  which  takes  the 
potassium  away  from  the  iodine  :  as,  soon  as  the  latter  becomes 
free,  it  produces  the  blue  color  with  the  starch  (§  91). 

If  we  suspend  a  bright  silver  coin  in  ozone,  it  soon  becomes 
tarnished.  If  we  smell  the  air  in  the  bottle,  we  find  that  it  has  a 
peculiar,  and  not  very  pleasant,  odor. 

It  has  been  found  that  these  same  phenomena  are  produced 
by  pure  oxygen  gas  through  which  electrical  sparks  have  been 
passed  (Fig.  36),  and  that  by  the  passage  of  such  sparks  the  vol- 
ume of  the  oxygen  is  diminished, 
while  its  weight  of  course  does  not 
change.  The  increase  in  density  so 
observed  has  shown  that  ozone  is 
half  again  as  heavy  as  oxygen  :  when 
ozone  is  heated,  it  is  converted  into 
ordinary  oxygen,  and  the  volume  is 
expanded  in  the  same  proportion. 
Chemists  have  consequently  been  led 
to  believe  that  while  ordinary  oxygen 
contains  two  atoms  in  its  molecule,  a 
molecule  of  ozone  contains  three  such 
atoms.  We  may  consider,  therefore, 
that  if  a  molecule  of  ordinary  oxygen 
is  represented  by  the  formula  O2,  O3 
represents  a  molecule  of  ozone. 

67.  Let  us  see  why  ozone  possesses 
more    active    powers    than    oxygen. 

When  we  pass  electric  sparks  through  oxygen,  we  decompose  its 
molecules,  and  the  energy  of  electricity  is  transferred  to  the  atoms, 
which  it  enables  to  combine  by  threes,  instead  of  by  twos.  Phos- 
phorus is  gradually  oxidized  by  oxygen,  but  one  atom  of  phos- 
phorus does  not  combine  with  whole  molecules  of  oxygen :  we 


FIG 


HYDROGEN    DIOXIDE.  55 

shall  in  time  learn  that  in  this  case  two  atoms  of  phosphorus  take 
three  atoms  of  oxygen  ;  that  would  be  a  molecule  and  a  half;  but, 
wl  ile  the  energy  developed  by  the  rapid  combustion  of  phosphorus 
appears  as  heat  and  light,  the  energy  developed  by  the  slow  com- 
bustion of  the  phosphorus  is  transferred  to  the  odd  atom  of  oxy- 
gen, and  enables  it  to  combine  with  two  other  atoms  set  free  from 
ID  tlecules  in  the  same  manne'r.  We  might  represent  this  by  our 

sy  nbols. 

6P         +        GO'2  3P203  +        O3 

Phosphorus,  Oxygen,  Phospkorus  trioxide,  Ozone, 

six  atoms.         six  molecules.  three  molecules.  one  molecule. 

As  ozone  contains  more  energy  than  oxygen,  we  naturally 
e>  pect  its  properties  to  be  more  energetic'. 

We  shall  have  occasion  to  study  many  actions  of  this  kind,  where 
tl-e  energy  evolved  by  the  combination  of  certain  atoms  is  trans- 
ft  -red  to  other  atoms,  giving  them  more  active  properties  than 
tl  ey  had  before.  . 

When  ozone  oxidizes  other  bodies,  in  most  cases  only  one  of  its 
at  3ins  is  used  in  the  oxidation ;  the  other  two  unite  to  form  a 
iDDlecule  of  oxygen. 

When  the  moist  potassium  iodide  was  decomposed  by  ozone, 
p<  tassium  hydrate  was  formed  ;  its  molecule  contains  KOH,  and 
w •}  see  that  the  water  present  must  have  taken  part  in  the  reac- 
tion, which  we  may  write 

2KI  +  H2Q  +  O3  =  2KOH  +  O2  +  I2 

Potassium  iodide.  Potassium  hydrate. 

68.  Ozone  is   produced   in  nearly  all   slow  combustions.     By 
cold  and  pressure  it  has   been  converted  into  a  sky-blue  liquid. 
It  is  destroyed,  that  is,  converted  into  oxygen,  by  a  temperature 
of  290°.     Its  oxidizing  powers  are  sometimes  employed  for  bleach- 
ing and  disinfecting,  the  ozone  in  these  cases  being  produced  by 
electricity. 

HYDROGEN  DIOXIDE,  H'O2. 

69.  We  introduce  some  pulverized  barium  dioxide,  a  compound 
whose  molecule  contains  one  atom  of  the  metal  barium  and  two 
atoms  of  oxygen,  into  a  small  flask  containing  some  cold  dilute  hy- 
drochloric acid  ;  as  the  solid  dissolves,  a  solution  of  barium  chloride 


56  LESSONS    IN    CHEMISTRY. 

is  formed,  while  the  hydrogen  of  the  hydrochloric  acid  and  the 
oxygen  of  the  barium  dioxide  combine  to  form  a  compound  called 
hydrogen  dioxide,  which  remains  dissolved  in  the  liquid. 

BaO2  +  2HC1  =         Bad2  +  H202 

Barium  dioxide.        Hydrochloric  acid.        Barium  chloride.        Hydrogen  dioxide. 

The  separation  of  the  hydrogen  dioxide  from  the  barium  chlo- 
ride is  not  an  easy  matter,  but  the  latter  compound  will  not  inter- 
fere with  our  experiments. 

We  pour  some  of  the  liquid  on  a  little  manganese  dioxide ;  at 
once  a  brisk  effervescence  takes  place,  and  by  the  aid  of  a  match- 
stick  bearing  a  spark,  we  are  shown  that  the  tube  is  filled  with 
oxygen.  The  hydrogen  dioxide  has  been  decomposed  into  water 
and  oxygen  ;  but  the  manganese  dioxide  remains  unchanged  ;  it  is 
probably  in  fact  converted  into  a  higher  oxide,  but  the  addi- 
tional oxygen  is  at  once  taken  away  from  this  oxide  by  another 
atom  of  oxygen  with  which  it  forms  a  molecule  of  the  gas. 

In  another  tube,  we  pour  a  little  of  our  solution  on  some  black 
lead  sulphide :  the  color  quickly  changes  to  white,  and  no  gas  is 
given  off,  for  the  lead  sulphide  is  converted  into  lead  sulphate, 
while  water  is  formed. 

PbS  +  4H202  =        PbSO4        +  4H20 

Lead  sulphide.  Lead  sulphate. 

We  now  pour  a  little  hydrogen  dioxide  into  some  purple 
solution  of  potassium  permanganate.  The  color  is  at  once  de- 
stroyed, and  the  liquid  becomes  colorless  ;  at  the  same  time  bubbles 
of  oxygen  are  disengaged,  and  may  be  identified  by  the  usual  test. 
In  this  case  an  atom  of  oxygen,  very  loosely  held  by  the  other 
atoms  in  the  hydrogen  dioxide,  has  combined  with  another  atom 
from  the  potassium  permanganate,  which  is  very  rich  in  oxygen, 
and  a  molecule  of  free  oxygen  is  given  off,  while  water  is  formed 
as  before. 

We  mix  some  of  the  hydrogen  dioxide  liquid  with  a  little 
yellow  solution  of  potassium  dichromate  ;  we  then  quickly  pour 
in  a  quantity  of  ether,  and  briskly  shake  the  tube  ;  the  ether 
being  lighter  than  the  water,  comes  to  the  top  of  the  latter,  in 
which  it  is  almost  insoluble,  and  this  layer  of  ether  has  a  dark 


CHLORINE.  57 

bin  3  color.  It  contains  perchromic  acid,  a  body  which  is  formed 
by  the  oxidation  of  the  potassium  dichromate  ;  but  with  hydrogen 
dioxide  this  perchromic  acid  behaves  just  like  potassium  perman- 
ganate ;  unless  it  is  at  once  removed  from  the  liquid  in  which  it  is 
for  ned,  its  oxygen  is  taken  away,  and  a  green  liquid  containing  a 
lover  oxide  of  chromium  is  obtained. 

'0.  We  may  then  conclude  that  hydrogen  dioxide  acts  in  three 
ways  with  other  substances  :  sometimes  it  is  reduced,  that  is,  part 
of  its  oxygen  is  taken  away,  while  the  other  body  remains  un- 
changed, as  is  the  case  with  manganese  dioxide  ;  sometimes  the 
sec  and  substance  is  oxidized,  as  with  the  lead  sulphide  and  potas- 
sium dichromate ;  sometimes  both  the  hydrogen  dioxide  and  the 
otl  er  body  are  deoxidized,  as  in  the  cases  of  potassium  perman- 
ga  late  and  perchromic  acid. 

Pure  hydrogen  dioxide  is  a  syrupy,  colorless  liquid,  without 
ou  >r,  and  having  a  density  of  1.45.  It  is  slowly  decomposed  into 
w;  ter  and  oxygen  at  ordinary  temperatures,  with  brisk  efferves- 
ce ice  at  100°,  and  explosively  if  dropped  on  a  surface  heated  to 
higher  temperatures. 

Hydrogen  dioxide  and  ozone  undergo  mutual  decomposition, 
water  and  free  oxygen  being  formed. 

H202  +      Q3     =  :     H20    +  202 

Hydrogen  dioxide.  Ozone.  Water.  Two  molecules  of  oxygen. 
A'Ve  must  consider  that  a  molecule  of  hydrogen  dioxide  is  formed  by  the 
un  on  of  two  atomic  groups,  each  containing  an  atom  of  oxygen  and  an  atom 
of  lydrogen.  The  oxygen  atoms  in  this  molecule  contain  more  energy  than 
tin  similar  atoms  in  molecules  of  water  and  of  free  oxygen,  and  this  extra 
em  rgy  is  manifested  when  the  hydrogen  dioxide  decomposes. 


LESSON    VIII. 

CHLORINE.— CHLORIDES. 

Atomic  weight,  35.5.  Symbol,  Cl. 

71.  The  element  chlorine  has  such  strong  affinities  for  other 
elements  that  it  does  not  exist  free  in  nature,  but  is  always  found 


58 


LESSONS    IN    CHEMISTRY. 


in  combination.  The  most  important  of  its  compounds  is  common 
salt,  which  contains  sodium  and  chlorine,  and  of  which  enormous 
quantities  exist  in  the  ocean,  and  in  salt  springs  and  salt  mines. 
We  do  not  usually  prepare  chlorine  directly  from  salt,  but  from 
hydrochloric  acid,  the  latter  being  prepared  from  the  salt  itself. 

We  mix  in  a  glass  flask  some  strong  hydrochloric  acid  with 
about  one-sixth  its  weight  of  manganese  dioxide,  and,  after  adapt- 
ing to  the  flask  a  cork  through  which  passes  a  tube  for  the  exit 
of  the  gas,  and  another  tube  called  a  safety-tube,  we  gently  heat 
the  mixture  over  a  flame  (Fig.  37).  The  safety-tube  (A),  which 


FIG.  37. 

is  bent  around  on  itself  and  has  a  little  bulb  blown  on  the  bend, 
enables  us  to  add  more  acid  if  necessary,  and  at  the  same  time  if 
there  should  be  too  much  pressure  in  the  flask  it  allows  the  gas 
to  escape  through  the  little  acid  which  we  must  pour  into  it: 
on  the  contrary,  when  the  flask  cools  and  the  gas  contracts  in  vol- 
ume, air  may  enter  through  the  safety-tube,  and  any  liquid  into 
which  we  may  wish  the  end  of  the  delivery-tube  to  dip,  will  not 
be  drawn  back  into  the  flask.  We  may  dry  our  chlorine  gas  by 
passing  it  through  a  bottle  containing  either  calcium  chloride  or 
strong  sulphuric  acid,  or  we  may  pass  it  directly  into  a  bottle. 


CHLORINE.  59 

Chiorine  dissolves  in  water,  and  we  collect  it  by  downward  dry 
displacement ;  for  it  is  a  heavy  gas,  and  when  we  pass  the  tube 
through  which  it  flows  to  the  bottom  of  a  jar,  the  chlorine  grad- 
ual y  forces  the  air  out  at  the  top.  We  might  collect  it  over  salt 
wa-er  in  the  pneumatic  trough,  as  it  does  not  dissolve  in  salt 
wirer.  We  can  easily  see  when  the  jar  is  full,  for  the  gas  has  a 
gn  enish-yellow  color.  While  we  are  filling  several  jars,  which 
we  cover  with  glass  plates  as  soon  as  they  are  filled,  we  may  ex- 
amine the  chemical  change  by  which  chlorine  is  formed.  Man 
ganese  dioxide  contains  two  atoms  of  oxygen,  and  this  oxygen 
coi  ibines  with  the  hydrogen  of  the  hydrochloric  acid,  forming 
wa  ;er.  Two  atoms  of  oxygen  require  four  atoms  of  hydrogen, 
an  I  for  these  four  atoms  we  will  need  four  molecules  of  hydro- 
ch  oric  acid,  each  of  which  contains  one  atom  of  chlorine  and  one 
of  hydrogen.  The  atom  of  manganese  combines  with  two  atoms 
of  chlorine,  forming  a  body  called  manganese  chloride,  and  as 
th  re  were  four  chlorine  atoms  in  the  hydrochloric  acid,  two  of 
tli>  se  will  pass  off  as  gas.  We  may  write  the  reaction, 

MnO2  +  4HC1  MnCl2  +  2H2Q  +  Cl* 

Ma  iganese  dioxide.        Hydrochloric  acid.        Manganese  chloride.  Chlorine. 

72.  Properties. — Chlorine  is  a  greenish-yellow  gas,  having  an 
unpleasant,  suffocating  odor.  We  must  be  careful  not  to  breathe 
it  n  a  too  undiluted  form,  for  it  causes  violent  coughing,  and  irri- 
tates the  lungs.  It  is  1.247  times  as  heavy  as  an  equal  bulk  of 
air,  or  35.5  times  as  heavy  as  an  equal  volume  of  hydrogen.  Its 
atomic  weight  is  also  35.5  :  there  are  many  other  elements  whose 
atcmic  weights  and  densities  (when  in  the  form  of  gas)  compared 
to  hydrogen  are  the  same,  and  we  must  suppose  that  the  mole- 
cules of  such  elements  are  like  those  of  hydrogen  in  that  each 
contains  two  atoms  (§  46).  Chlorine  dissolves  in  water:  at  ordi- 
nary temperatures,  one  litre  of  water  will  dissolve  about  two 
and  a  half  litres  of  the  gas.  It  may  be  liquefied  at  15°  by  a 
pressure  of  four  atmospheres,  that  is,  four  times  as  great  as  the 
ordinary  pressure  of  the  air. 

Chlorine  possesses  very  great  affinity  for  the  other  elements, 
and  the  compounds  which  it  forms  with  them  are  called  chlorides. 


60 


LESSONS    IN    CHEMISTRY. 


Over  one  of  our  jars  of  the  gas  we  place  a  piece  of  coarse  wire 
gauze,  through  which  we  spriukle  some  finely-powdered  antimony. 
Each  little  particle  burns,  and  we  have  a  shower  of  fire,  while  a 
heavy  cloud  of  white  smoke  settles  in  the  jar:  this  smoke  is 
antimony  chloride.  Into  another  jar  we  throw  some  pieces  of 
Dutch  leaf,  a  very  thin  brass  used  for  cheap  gilding :  this  also 
burns,  and  the  copper  and  zinc  of  which  the  Dutch  metal  was 
composed  are  converted  into  copper  chloride  and  zinc  chloride. 
We  may  burn  some  thin  copper  in  the  same  manner.  We  put  a 
small  piece  of  phosphorus  in  a  deflagrating-spoon,  and  lower  this 
into  another  jar :  it  burns  with  a  pale  flame  into  phosphorus 
chloride. 

73.  Of  all  the  elements,  hydrogen  is  that  for  which  chlorine 
possesses  the  most  remarkable  affinities.  In  a  room  lighted  only 
by  a  candle,  we  have  mixed  over  salt  water  equal  volumes  of 
chlorine  and  hydrogen,  and,  after  drying  this  mixture  by  passing 
it  through  a  tube  containing  pumice-stone  and  sulphuric  acid,  we 
have  filled  with  it  some  little  bulbs,  blown  on  thin  glass  tubes, 
and  then  sealed  the  ends  of  the  tubes  with  little  plugs  of  paraffin. 
It  is  easy  to  fill  the  bulb ;  we  connect  one  end  of  it  by  a  rubber 

tube  on  which  is  a  pinch 
(A),  to  the  tube  of  the 
bell-jar  in  which  the  mix- 
ture is  made;  then  on 
pressing  the  jar  into  the 
salt  water  and  loosing  the 
pinch,  the  gas  is  forced 
through  the  bulb  (Fig. 
38).  We  keep  these  bulbs 
carefully  covered  from  the 

light.  We  now  uncover  one,  put  it  behind  a  sheet  of  glass,  and 
then,  standing  at  a  little  distance,  burn  a  piece  of  magnesium  wire. 
Instantly  there  is  an  explosion  ;  the  hydrogen  and  chlorine  have 
combined.  The  combination  is  brought  about  in  the  same  manner 
by  direct  sunlight,  and  more  gradually  by  diffuse  daylight. 

Chlorine  does  not  support  ordinary  combustion,  for  it  does  not 


FIG.  38. 


CHLORINE. — CHLORIDES.  61 

combine  directly  with  carbon,  and  ordinary  combustibles  contain 
hy  Irogen  and  carbon  ;  but  their  hydrogen  may  burn  in  chlorine. 
W-3  put  a  lighted  taper  into  a  jar  of  chlorine,  and  the  flame  be- 
comes red  and  smoky :  the  chlorine  combines  with  the  hydrogen 
of  the  wax,  but  the  carbon  separates  in  the  form  of  smoke. 

Chlorine  even  decomposes  many  compounds  containing  hydro- 
g<  i,  taking  away  that  element  to  form  hydrochloric  acid.  The 
so  ution  of  chlorine  in  water  is  decomposed  by  sunlight,  the  oxy- 

gci  being  set  free. 

2C12  +  2II20  =  4HC1  +  O2 

Into  a  jar  with  straight  sides,  filled  with  chlorine,  we  rapidly 
in  reduce  a  paper  saturated  with  turpentine,  and  quickly  replace 
tli  j  cover  of  the  jar.  There  is  a  flash  of  red  light,  and  a  cloud  of 
sn  oke.  Turpentine  is  a  compound  of  carbon  and  hydrogen  only  : 
th  3  chlorine  combines  with  the  hydrogen,  and  the  carbon  forms 
tli  3  smoke.  We  find  after  the  experiment  that  the  paper  is  not 
bi  rned  :  we  use  a  plain  straight  jar,  because  it  is  easily  cleaned  by 
rubbing  with  a  little  turpentine. 

We  pour  some  blue  litmus-water  into  a  jar  of  chlorine ;  the 
bl  le  liquid  becomes  colorless.  In  another  jar  we  suspend  a  piece 
of  moist  colored  calico,  and  it  quickly  fades.  Chlorine  possesses 
bl  Caching  properties,  and  these  properties  are  due  to  the  decompo- 
sition of  the  dye-stufts,  nearly  all  of  which  contain  hydrogen  that 
the  chlorine  may  remove.  For  the  same  reason  chlorine  is  a  val- 
ui  ble  disinfectant,  for  most  unpleasant  and  unwholesome  odorous 
matters  are  compounds  of  hydrogen. 

74.  Chlorides. — The  binary  compounds  of  chlorine  are  called 
chlorides,  and  the  same  prefixes  which  are  used  for  the  names  of 
the  oxides  are  employed  also  to  indicate  the  number  of  chlorine 
atoms  in  a  molecule  of  the  compound  ;  thus,  phosphorus  trichloride 
contains  PCI3.  In  general,  these  prefixes  are  used  to  indicate  the 
number  of  atoms  of  the  second  named  element  with  which  one  or 
more  atoms  of  that  first  named  are  combined.  When  there  are 
only  two  chlorides  which  are  important,  the  terminations  ous  and 
ic  designate  which  contains  the  greatest  and  the  least  proportion 
of  chlorine  (see  §  64).  Mercurous  chloride  is  Hg'2Cl2 ;  mercuric 

6 


62  LESSONS    IN    CHEMISTRY. 

chloride  is  HgCP  :  this  nomenclature  also  is  of  general  appli- 
cation. 

Among  the  chlorides  of  the  non-metallic  elements,  hydrochloric 
acid  is  the  most  important. 

The  metallic  chlorides  are  all  soluble  in  water,  with  the  excep- 
tion of  silver  chloride,  AgCl,  mercurous  chloride,  Hg2Cl2,  and 
cuprous  chloride,  Cu2Cl2.  Lead  chloride  is  only  slightly  soluble. 
Some  chlorides  are  decomposed  by  water,  and  in  such  a  case  part 
or  all  of  the  chlorine  combines  with  hydrogen,  forming  hydro- 
chloric acid.  Thus,  phosphorous  chloride,  PCI3,  yields  phosphorous 
acid  and  hydrochloric  acid. 

2PC13  +  3H20  =       2H3P03         +  6HC1 

Phosphorous  chloride.  Phosphorous  acid.        Hydrochloric  acid. 

75.  We  pour  a  few  drops  of  a  solution  of  silver  nitrate  in  pure 
water  into  some  water  in  which  common  salt,  which  is  sodium 
chloride,  has  been  dissolved.  At  once  a  white  precipitate  forms, 
for,  while  sodium  nitrate  now  exists  in  solution,  silver  chloride  is 
formed,  and  this  is  insoluble. 

AgNO3       +  NaCl  =         NaNO3         +         AgCl 

Silver  nitrate.        Sodium  chloride.        Sodium  nitrate.        Silver  chloride. 

The  precipitate  darkens  on  exposure  to  light,  and  this  reaction 
enables  us  to  determine  whether  a  body  contains  or  does  not  con- 
tain a  chloride.  All  solutions  of  chlorides  give  the  white  precipi- 
tate, which,  we  may  add,  dissolves  if  we  pour  off  most  of  the 
liquid  and  then  shake  the  white  powder  with  strong  ammonia- 
water. 


LESSON    IX. 
HYDROCHLORIC   ACID.— ACIDS.— SALTS. 

76.  Hydrochloric  Acid,  HC1. — We  have  seen  that  this  com- 
pound is  formed  by  the  direct  union  of  chlorine  and  hydrogen, 
and  by  the  action  of  water  on  certain  chlorides.  Many  chlorides 
are  decomposed  by  water  at  high  temperatures,  and  in  this  manner 
some  mineral  chlorides  existing  in  the  rocks  cause  hydrochloric 


HYDROCHLORIC    ACID. 


63 


acii  to  be  formed  in  certain  volcanic  regions,  where  it  mixes  with 
tin  other  gases  that  are  emitted. 

77.  Preparation. — Hydrochloric  acid  is  made  by  the  action  of 
su  phuric  acid  on  common  salt,  the  sodium  of  the  salt  changing 
pk'ces  with  the  hydrogen  of  the  sulphuric  acid. 

We  put  some  pieces  of  rock-salt  in  a  flask  like  that  in  which 
wt  made  chlorine,  and,  if  we  wish  a  solution  of  the  gas,  we  con- 
ni  >t  our  delivery-tubes  with  a  series  of  bottles  containing  water, 
th  'ough  which  the  gas  will  be  forced  to  bubble  (Fig.  39).  If  we 

0 


FIG.  39. 

wish  the  dry  gas,  we  dry  it  as  we  did  the  chlorine.  When  all  is 
ready,  we  pour  through  the  safety-tube  sulphuric  acid  which  we 
have  previously  diluted  with  an  equal  volume  of  water,  and  im- 
mediately the  gas  begins  to  come  off.  When  the  reaction  becomes 
tranquil,  we  must  heat  the  mixture. 

One  molecule  of  sulphuric  acid  contains  two  atoms  of  hydrogen, 
and  may  be  made  to  yield  one  or  two  molecules  of  hydrochloric 
acid,  by  reacting  with  one  or  with  two  molecules  of  salt. 

XiiCl          +        H2S04  HCl  .+  NaHSO4 

Sodium  chloride.      Sulphuric  acid.      Hydrochloric  acid.      Sodium  acid  sulphate. 

2NaCl  +  H2SO*  -  2HCI   +         Na2S04 

Sodium  sulphate. 


64  LESSONS   IN   CHEMISTRY. 

This  reaction  is  operated  on  an  enormous  scale  in  Europe,  where 
the  sodium  sulphate  is  afterwards  heated  with  chalk  and  converted 
into  sodium  carbonate. 

78.  Properties. — Hydrochloric  acid  is  a  colorless,  pungent,  and 
suffocating  gas.     Its  density  compared  to  hydrogen  is  18.33,  suf- 
ficiently near  that  which  would  be  indicated  by  half  its  molecular 
weight,  which   is  36.5  (see  §  48).     It  is  very  soluble  in  water, 
and  if  under  the  surface  of  water  we  remove  the  cork  from  a  bot- 
tle filled  with  the  gas,  the  water  at  once  rises  and  fills  the  bottle. 
At  0°  one  litre  of  water  will  dissolve  500  litres  of  hydrochloric 
acid.     The  strongest  hydrochloric  acid  of  commerce,  commonly 
called  muriatic  acid,  contains  about  34  per  cent,  of  the  gas.     Like 
the  gas,  it  produces  fumes  in  the  air  by  condensing  the  moisture 
in  the  atmosphere. 

Hydrochloric  acid  is  a  strong  acid.  A  drop  or  two  of  the  solu- 
tion will  redden  a  large  quantity  of  blue  litmus.  '  We  slowly  pour 
some  hydrochloric  acid  into  a  strong  solution  of  sodium  hydrate : 
a  white  powder  soon  separates,  and  we  can  satisfy  ourselves  by 
tasting  it  that  this  is  common  salt.  Water  also  is  formed. 

NaOH         +  HC1  =  H>0  +          NaCl 
Sodium  hydrate.  Sodium  chloride. 

With  oxides  of  the  metals,  hydrochloric  acid  acts  in  the  same 
manner,  water  and  a  chloride  being  formed. 

HgO          +  2HC1  =          HgCl2          +  H20 
Mercuric  oxide.  Mercuric  chloride. 

We  have  seen  that  zinc  liberates  the  hydrogen  from  hydro- 
chloric acid  :  many  other  metals  act  likewise. 

ACIDS   AND    SALTS. 

79.  An  acid  is  a  compound  containing  hydrogen  which  is  ca- 
pable of  being  replaced  by  a  metal,  forming  a  body  which  is  called 
a  salt.     Although  salts  may  be  formed  in  various  manners,  we  have 
an  exact  definition  :  a  salt  represents  an  acid  whose  hydrogen  has 
been  partly  or  wholly  replaced  by  metal.     Hydrochloric  acid  is  an 
example  of  a  binary  acid,  but  the  few  binary  acids  which  we  shall 
study  have  not  all  as  energetic  properties  as  hydrochloric  acid. 
The  salts  formed  by  hydrochloric  acid  are  of  course  the  chlorides. 


IIYPOCHLOROUS    OXIDE    AND    ACID.  65 

30.  Hypochlorous  Oxide  and  Acid.— When  chlorine  is  passed 
ov3r  cooled  mercuric  oxide,  mercuric  chloride  is  formed,  and  the 
oxygen  which  separates  from  the  mercury  combines  with  chlo- 
rh  e,  forming  a  gas  which  may  be  condensed  to  a  yellow  liquid 
by  passing  it  into  a  bottle  surrounded  by  a  freezing  mixture  of 
ice  and  salt. 

HgO  +      2Cl2  =         HgCi2  +  C120 

Mercuric  oxide.  Mercuric  chloride.  Hypochlorous  oxide. 

This  is  hypochlorous  oxide ;  it  is  a  dangerous  body,  and  often 
explodes  without  warning. 

It  reacts  with  water  in  a  manner  which  we  must  study.  A 
m  >lecule  of  the  oxide  and  a  molecule  of  water  interchange  a  chlo- 
ri-ie  atom  for  a  hydrogen  atom,  and  a  compound  called  hypochlo- 
r<  is  acid  is  formed. 

C10C1  +  HOH    =  HOCl  +  C10H 

Hypochlorous  oxide.        Water.        Hypochlorous  acid.         Hypochlorous  acid. 

This  is  an  oxygen  acid,  and  we  may  consider  that  it  is  com- 
p»  sed  of  an  atom  of  chlorine  combined  with  the  residue  of  a  inol- 
cc  ale  of  water  from  which  one  atom  of  hydrogen  has  been  re- 
in >ved.  This  residue  would  be  OH,  and,  because  the  atom  of 
o>ygen  has  not  enough  hydrogen  to  satisfy  the  affinities,  it  is  not 
a  molecule ;  it  cannot  exist  except  as  part  of  a  molecule ;  that  is, 
combined  with  some  other  atom.  It  is  called,  for  convenience' 
salve,  hydroxylj  and  all  oxygen  acids  contain  this  group  of  two 
at  >ms,  hydroxyl.  Indeed,  all  of  the  compounds  we  call  hydrates 
contain  the  group  hydroxyl:  thus,  potasssium  hydrate  is  KOFI. 

81.  We  have  had  occasion  to  notice  the  names  hydrochloric 
acid,  hypochlorous  acid,  sulphuric  acid.  We  have  seen  that  hy- 
drochloric acid  produces  binary  salts :  the  names  of  binary  coin- 
pounds,  with  the  exception  of  acids,  end  in  ide,  and  we  can  now 
even  understand  that  a  sulphide  is  a  compound  containing  sulphur 
arid  one  other  element.  But  hypochlorous  acid  and  sulphuric 
acid  are  not  binary  compounds :  they  may  be  formed  respectively 
by  the  action  of  hypochlorous  and  sulphuric  oxides  on  water.  The 
first  of  these  actions  we  have  studied  :  the  second  we  may  write 

SO*  +  R2Q  =  H'SO*. 
e  6* 


66  LESSONS    IN    CHEMISTRY. 

When  the  hydrogen  of  either  of  these  oxygen  acids  is  replaced 
by  metal,  how  shall  we  name  the  resulting  salts?  Chemists  have 
agreed  that  the  termination  ic  shall  be  changed  to  ate.  and  ous 
shall  be  changed  toite.  This  is  a  simple  nomenclature.  The  salts 
of  sulphuric  acid  must  be  sulphates  ;  those  of  nitric  acid,  nitrates  ; 
those  of  permanganic  acid,  permanganates ;  those  of  hypochlorous 
acid,  hypochlorites  ;  those  of  sulphurous  acid,  sulphites.  We  see 
also  that  the  chlorates  must  be  the  salts  of  chloric  acid ;  the  ar- 
senites,  those  of  arsenious  acid. 

82.  Hypochlorites.— Solutions  of  the  hypochlorites  of  potas- 
sium and  sodium  are  useful  as  disinfecting  and  bleaching  liquids. 
They  are  made  by  passing  chlorine  gas  into  a  rather  dilute  solu- 
tion of  potassium  hydrate  or  sodium  hydrate ;  at  the  same  time 
water  is  formed,  and  a  chloride,  which  remains  in  solution. 

2NaOH         +  Cl2  =  NaOCl  +          NaCl          +  H20 

Sodium  hydrate.  Sodium  hypochlorite.      Sodium  chloride. 

Such  a  liquid  quickly  removes  the  stains  of  wine  and  fruits 
from  linen,  and  also  deodorizes  offensive  matters. 

Bleaching  powder,  or  chlorinated  lime,  is  made  by  passing  chlo- 
rine gas  over  slaked  lime.  Its  solutions  contain  calcium  hypo- 
chlorite, Ca(ClO)2,  and  may  be  substituted  for  the  liquids  which 
we  have  just  mentioned.  The  bleaching  and  disinfecting  by  these 
substances  are  due  to  their  decomposition,  which  we  may  suppose 
first  sets  free  hypochlorous  acid,  and  this  attacks  the  coloring 
matter  or  offensive  substance,  removing  hydrogen  ;  the  chlorine 
atom  will  take  one  atom  of  hydrogen,  forming  hydrochloric  acid, 
and  the  group  OH  takes  another  atom,  forming  water.  We  may 
understand  this  by  examining  the  reaction  between  hydrochloric 
and  hypochlorous  acids,  which  yields  chlorine  and  water. 
HC10  +  HC1  =  H*0  +  Cl2 

83.  Chlorates, — We  pass  a  current  of  chlorine   gas   into  a 
strong  solution  of  potassium  hydrate,  and  a  white  solid  matter 
soon  appears  in  the  liquid ;  when  this  no  longer  increases  in  bulk, 
we  stop  the  chlorine,  heat  the  liquid  until  it  boils,  and  if  all  of  the 
solid  dissolves,  we  evaporate  it  until  a  considerable  quantity  of 
this  matter  again  separates.     We  now  allow  it  to  settle  a  moment, 


CHLORIC    ACID. — CHLORATES.  67 

and  pour  off  the  clear  liquid :  as  this  cools,  shining  little  crystals 
separate  in  rhomboidal  plates.  These  are  potassium  chlorate,  and 
we  have  been  obliged  to  separate  them  from  potassium  chloride, 
which,  together  with  water,  is  also  formed  during  the  experiment. 

6KOH          +  3C12  5KC1  +         KC103  +  3H20 

Po  assium  hydrate.  Potassium  chloride.        Potassium  chlorate. 

Potassium  chlorate  is  the  most  important  salt  of  chloric  acid, 
H  CIO3,  which  we  might  prepare  from  the  salt  by  a  troublesome 
pi  jcess.  Potassium  chlorate  is  not  very  soluble  in  cold  water, 
bi  t  is  very  soluble  in  boiling  water. "  Its  solution  is  excellent  as  a 
g;rgle  for  sore  throat,  but  must  not  be  swallowed,  for  it  is  poison- 
01  s.  We  have  seen  that  potassium  chlorate  is  decomposed  by 
hi  at,  yielding  oxygen  :  it  readily  gives  up  its  oxygen,  for  the 
cMorine  has  a  much  stronger  affinity  for  the  potassium  than  for 
tie  oxygen,  which  appears  to  hold  the  chlorine  and  potassium 
at  jms  together. 

84.  Chloric  acid,  which  would  be  set  free  by  the  action  of 
st  -onger  acids  on  potassium  chlorate,  is  at  once  decomposed  under 
si  eh  circumstances  if  oxidizable  substances  be  present.  On  a 
iiKXture  of  equal  parts  of  potassium  chlorate  and  sugar,  powdered 
separately,  we  let  fall  a  drop  of  strong  sulphuric  acid.  The  mix- 
ture at  once  takes  fire  and  burns  vividly,  the  potassium  chlorate 
furnishing  the  oxygen  for  the  combustion  of  the 
sugar. 

Into  a  tall  jar,  filled  with  water,  we  throw  some 
crystals  of  potassium  chlorate,  and  on  them  a  small 
piece  of  phosphorus  ;  then,  by  means  of  a  funnel- 
tube  which  passes  to  the  bottom  of  the  jar,  we  pour 
some  strong  sulphuric  acid  on  the  chlorate.  The 
chloric  acid  set  free  is  decomposed  by  the  phos- 
phorus and  causes  its  combustion  under  the  water 
(Fig.  40). 

We  put  into  a  mortar  a  piece  of  sulphur  about  as 
large  as  a  match-head,  and  a  crystal  of  potassium 
chlorate  of  the  same  size  ;  then  we  rub  them  briskly  together,  being 
careful  to  keep  the  mortar  fnr  enough  from  the  face,  and  soon  there 


68  LESSONS    IN    CHEMISTRY. 

is  a  loud  report ;  the  sulphur  has  been  oxidized  and  the  potassium 
chlorate  decomposed.  If  we  used  larger  quantities  of  these  sub- 
stances in  our  experiment,  we  might  break  the  mortar,  and  possibly 
injure  our  person. 


LESSON    X. 
BROMINE.— IODINE.— FLUORINE. 

85.  Bromine,  Br  —  80. — In  a  long  tube  closed  at  one  end, 
we  dissolve  in  a  little  water  a  few  crystals  of  a  white  substance, 
called  potassium  bromide,  and  then  pour  in  some  chlorine-water, 
which  we  have  prepared  by  passing  chlorine  through  water  con- 
tained in   bottles  such   as  were  used  in  the  preparation  of  the 
solution  of  hydrochloric  acid  :  we  now  add  a  considerable  propor- 
tion of  ether,  and  shake  the  tube  after  closing  it  with  the  finger. 
The  liquid  becomes  brown,  and  after  standing  a  few  minutes,  the 
ether,  which  is  not  very  soluble  in  water,  comes  to  the  surface, 
and  its  color  is  red,  while  the  water  has  become  colorless.     The 
potassium  bromide,  a  compound  of  potassium  and  bromine,  has 
been  decomposed  by  the  chlorine,  and  potassium  chloride  formed 
in  the  solution,  while  the  bromine  set  free  has  been  dissolved  by 
the  ether,  in  which  it  is  much  more  soluble  than  in  water.     We 
may  write  the  reaction, 

2KBr          +  Cl2     =  =     2KC1  +       Br* 

Potassium  bromide.  Potassium  chloride.        Bromine. 

86.  The  compounds  of  bromine  with  potassium,  sodium,  and 
magnesium,  which  compounds  are  called  bromides  of  those  metals, 
are  found  in  the  waters  of  many  salt  springs,  and  exist  in  small 
quantity  in  the  water  of  the  ocean.     As  they  are  much  more 
soluble  in  water  than  common  salt,  they  remain  dissolved  when 
most  of  the  salt  has  been  separated  by  evaporating  the  liquid,  and 
from  their  concentrated  solution  so  obtained  the  bromine  is  sepa- 
rated by  heating  the  liquid  with  sulphuric  acid  and  manganese 


BROMINE. — IODINE.  69 

dioxide.  Supposing  all  of  the  bromine  to  exist  as  potassium 
brc  mide,  manganese  sulphate,  potassium  sulphate,  and  water  are 
formed  at  the  same  time,  while  the  bromine  distils,  and  is  con- 
densed in  suitable  apparatus. 

2KBr          +  MnO2       +  2H2S04     =  K2S04        +     MnSO*  +  H20  +  Br2 
:'otassium       Manganese       Sulphuric        Potassium  Manganese 

bromide.  dioxide.  acid.  ^'ilphate.  sulphate. 

37.  Bromine  is  a  dark-red  liquid,  having  an  exceedingly  irri- 
tating  odor.  Its  density  is  2.99.  It  freezes  at  — 24°,  and  boils  at 
6.'  D  ;  it  is  very  volatile  at  ordinary  temperatures.  It  dissolves  in 
about  thirty  times  its  weight  of  water  at  15°,  and  is  quite  soluble 
in  ether,  chloroform,  and  carbon  disulphide,  liquids  which  dissolve 
m\ny  substances  that  are  not  soluble  in  water. 

Bromine  closely  resembles  chlorine  in  its  chemical  reactions, 
bi<t  its  affinities  are  not  as  powerful.  Its  solution  in  water  will 
bl  -ach  litmus,  and  other  coloring  matters,  but  more  feebly  than 
cl  lorine.  We  pour  a  little  bromine  into  a  deep  test-tube  and 
di  ip  in  a  small  piece  of  warm  thin  sheet  copper,  which  is  instantly 
ci  averted  into  copper  bromide  with  the  production  of  heat  and 
Ikht. 

Bromine  combines  with  hydrogen,  forming  hydrobromic  acid, 
II  Br,  a  gas  which  dissolves  in  water,  and  undergoes  reactions 
similar  to  those  of  hydrochloric  acid. 

Bromine  is  exceedingly  corrosive  to  animal  tissues,  and  is  some- 
times employed  as  a  caustic  in  surgery.  It  also  disinfects  like 
chlorine. 

The  atomic  weight  of  bromine  is  80,  and  the  density  of  its 
vapor  compared  to  hydrogen  is  also  80,  showing  that  a  molecule 
of  bromine  contains  two  atoms. 

88.  Iodine,  I  =  127.— In  a  tube  like  that  which  we  used  in 
the  experiment  with  potassium  bromide,  we  dissolve  a  little  potas- 
sium iodide  in  water,  add  chlorine-water  as  before,  and  then,  in- 
stead of  ether,  we  pour  in  some  carbon  disulphide.  After  shaking 
the  tube,  and  allowing  it  to  stand,  the  carbon  disulphide,  being 
heavier  than  the  water,  is  found  at  the  bottom  with  a  beautiful 
purple  color.  Were  we  to  pour  off  the  watery  liquid  and  allow 


70  '  LESSONS    IN    CHEMISTRY. 

this  carbon  disulphide  to  evaporate  in  a  shallow  dish,  it  would  leave 
a  brownish-gray  matter,  which  is  iodine,  and  which  the  chlorine 
has  driven  out  of  the  potassium  iodide,  just  as  it  separated  the 
bromine  from  the  potassium  bromide. 

89.  Like  bromine,  iodine  is  found  combined  with  potasssium, 
sodium,  and  magnesium  in  the  waters  of  some  springs,  and  in  sea- 
water.     It  also  exists  in  small   quantity  in  the  sodium  nitrate 
found  in  large  deposits  in  Chili,  and,  being  very  soluble  in  water, 
remains  in   the  mother-liquor,   as  it  is  called,  from  which   this 
sodium  nitrate   has  been  crystallized  for   its  purification.     It  is 
obtained  from  these  liquids,  and  from  the  ashes  of  sea-weeds ;  the 
sea-weeds  are  burned,  and  the  iodides  which  are  dissolved  out  of 
the  ashes  by  water,  are  treated  just  as  the  bromides  are  treated 
for  the  preparation  of  bromine.      Iodine  may  also  be  separated  by 
adding  nitric  acid  to  the  solution  of  an  iodide,  and  we  may  make 
the  experiment  by  pouring  a  little  nitric  acid  on  some  potassium 
iodide  solution  in  a  test-tube.     Potassium  nitrate  is  formed,  and 
iodine  deposits  as  a  dark  powder :  the  red  vapors  that  are  given 
off  are  a  compound  of  nitrogen  and  oxygen,  which  we  will  study 
in  good  time. 

90.  Iodine  is  purified  by  sublimation  ;  that  is,  heating  it,  and 
condensing  the  vapor.     When  pure,  it  is  in   crystalline,  bluish- 
gray  plates,  much  like  scales  of  plumbago.     Its  density  is  4.95. 
It  melts  at  107°,  and  boils  at  175°.     We  carefully  heat  a  few 
small  scales  of  iodine  in  a  large  glass  flask,  which  soon  becomes 
filled  with  a  magnificent  purple  vapor.     This  vapor  is  so  heavy 
that  we  may  pour  it  out  on  a  piece  of  cold  glass,  where  it  con- 
denses in  minute  crystals.     The  density  of  this  vapor  compared 
to  hydrogen  is  127,  and,  the  atomic  weight  being  127,  we  see 
that  the  iodine  molecule  contains  two  atoms. 

Iodine  is  very  slightly  soluble  in  water  :  one  part  of  iodine  re- 
quires 7000  parts  of  water  to  dissolve  it,  and  yet  the  solution  has 
a  distinct  brown  color.  It  dissolves  readily  in  alcohol,  ether, 
chloroform,  and  carbon  disulphide,  and  the  color  of  the  solution 
depends  on  the  solvent;  that  in  alcohol  is  brown,  but  that  in 
chloroform  is  violet. 


FLUORINE.  71 

9 1.  We  have  made  some  thin  starch  paste  by  boiling  starch 
with  water,  and  we  pour  some  of  this  into  two  test-tubes  :  to  the 
first  we  add  a  few  drops  of  a  solution  of  iodine  in  water,  and  the 
liqu  d  becomes  dark  blue ;  to  the  other  we  add  a  drop  or  two  of  a 
solo  .ion  of  potassium  iodide,  and  no  color  is  produced.  Starch  is 
dyeu  a  blue  color  by  iodine,  but  the  iodine  must  be  free ;  on  add- 
iug  a  few  drops  of  chlorine-water  to  the  second  tube  the  potassium 
is  i  -moved  from  the  iodine^  and  the  blue  color  at  once  appears. 
This  is  the  test  for  iodine. 

]  jdine  combines  with  hydrogen  to  form  hydriodic  acid,  HI,  a 
ga*  whose  properties  are  much  like  those  of  hydrochloric  acid.  It 
is  nade  by  heating  water  with  iodine  and  amorphous  phos- 
ph(  nis. 

','  .  Analogies  of  Cl,  Br,  and  I. — On  comparing  the  three  elements  which 
we  lave  just  considered,  we  find  that  while  one  is  a  gas,  another  liquid,  and 
the  hird  solid,  still  the  corresponding  compounds  formed  by  each  are  much 
alii  •  in  chemical  nature;  that  is,  the  composition  and  reactions  of  the  mole- 
cult  .  The  compounds  with  hydrogen  each  contain  one  atom  of  hydrogen  corn- 
bin  d  with  one  of  the  other  element :  if  the  power  to  combine  with  one  atom 
of  i  ydrogen  be  taken  as  the  measure  of  the  combining  power  of  any  atom, 
the  atoms  of  chlorine,  bromine,  and  iodine  must  have  equal  powers.  Since 
an  ;  torn  of  each  of  these  elements  combines  with  only  one  atom  of  hydrogen, 
the  are  said  to  be  monatonric  elements  in  their  compounds  with  hydrogen. 
But  their  affinities,  or  energies  of  combination,  for  hydrogen  are  not  alike: 
chl<  rine  will  take  the  hydrogen  away  from  hydrochloric  acid,  and  bromine 
will  take  it  away  from  hydriodic  acid.  This  is  also  the  order  of  their  affinity 
for  the  metals,  but  in  the  number  of  atoms  of  either  chlorine,  bromine,  or 
iodine  which  will  combine  with  one  atom  of  another  element,  the  three  are 
exactly  alike. 

I?i  this  last  respect  the  next  element  resembles  the  three  which  we  have  just 
studied. 

1>3.  Fluorine,  Fl. — We  have  evenly  coated  one  side  of  a  glass 
pla:e  with  wax,  and  in  the  wax  we  trace  a  design  with  a  sharp 
point,  taking  care  that  our  lines  go  quite  through  to  the  glass. 
In  a  shallow  dish  made  of  sheet  lead,  we  mix,  by  the  aid  of  a 
wooden  stick,  some  powdered  fluor-spar,  which  is  a  mineral,  with 
strong  sulphuric  acid  ;  ovej:1  this  we  place  our  glass  containing  the 
design,  with  the  waxed  side  down,  and  we  gently  warm  the  dish 
(Fig.  41).  In  a  few  minutes  we  remove  the  glass,  and,  after 


72  LESSONS    IN    CHEMISTRY. 

gently  warming  it,  rub  off  the  wax :  we  find  that  the  design  is 
permanently  etched  into  the  glass.  The  fluor-spar  is  a  compound 
of  the  elements  fluorine  and  calcium,  and  the  sulphuric  acid  has 


FIG.  41. 

decomposed  it,  forming  a  vapor  called  hydrofluoric  acid,  a  com- 
pound of  hydrogen  and  fluorine. 

CaFP  +         H2S04         =  CaSO4         +  2HF1 

Calcium  fluoride.        Sulphuric  acid.        Calcium  sulphate.        Hydrofluoric  acid. 

Hydrofluoric  acid  may  be  condensed  to  a  liquid,  and  it  may  be 
dissolved  in  water,  but  neither  the  liquid  nor  the  solution  can  be 
kept  in  glass  bottles,  because  fluorine  has  an  extraordinary  affinity 
for  the  element  silicon  which  forms  part  of  the  glass,  and  it  would 
combine  with  that  element,  destroying  both  bottle  and  acid.  It 
is  to  this  affinity  that  we  owe  the  etching  of  our  glass  plate. 
Bottles  of  india-rubber  or  of  lead  are  used  to  contain  hydrofluoric 
acid,  for  it  does  not  attack  those  substances.  The  graduations  on 
delicate  chemical  apparatus,  such  as  the  eudiometers  we  have  seen, 
are  etched  into  the  glass  by  this  acid.  Hydrofluoric  acid  is  very 
corrosive,  and  we  must  be  careful  in  its  use. 

The  powerful  affinities  of  fluorine  have  thus  far  prevented  chemists  from 
separating  the  element  and  studying  its  properties  ;  but,  since  we  know  that  the 
molecular  weight  of  hydrofluoric  acid  is  20,  and  have  reason  to  believe  that 
the  molecule  contains  only  one  atom  of  hydrogen,  we  conclude  that  the  atomic 
weight  of  fluorine  is  19. 

Besides  fluor-spar,  there  is  another  important  compound  of  fluorine  found 
in  nature;  it  is  the  mineral  cryolite,  which  is  a  double  compound  of  sodium 
fluoride  and  aluminium  fluoride. 


SULPHUR. — HYDROGEN    SULPHIDE. 


73 


LESSON    XL 
SULPHUR.— HYDROGEN   SULPHIDE. 

94.  Sulphur,  S  =  32. — We  are  all  familiar  with  sulphur,  or 
bi  mstone.  In  some  localities  it  is  found  pure  or  very  impure 
at  1  mixed  with  the  soil:  especially  is  this  the  cas~e  in  volcanic 
coantries.  Besides  this  free  or  native  sulphur,  as  it  is  called,  sul- 


phur is  found  combined  with  many  metals,  and  the  compounds 
aro  called  sulphides. 

Crude  sulphur  comes  in  large  quantities  from  Sicily,  where  it 
is  obtained  by  distilling  it  from  the  earthy  matters  with  which  it 
is  mixed.  It  is  refined  by  again  distilling  it  in  an  apparatus  con- 
sisting of  an  iron  boiler  (A,  Fig.  42),  above  which  is  a  reservoir 
(C)  where  the  sulphur  is  first  melted  by  the  waste  heat,  and  from 
which  it  runs  into  the  boiler.  The  sulphur  vapor  enters  a  large 
D  7 


74  LESSONS    IN   CHEMISTRY. 

chamber  (B),  and  after  condensing*  runs  down  on  the  floor,  which 
is  inclined  so  that  the  melted  sulphur  may  be  drawn  off  at  a  tap 
(H).  While  the  walls  of  this  chamber  are  yet  cold,  the  sulphur 
condenses  in  a  fine  yellow  powder,  which  is  sold  as  flowers  of  sul- 
phur;  but  when  the  chamber  becomes  heated,  the  condensed  sul- 
phur melts,  and  after  being  drawn  from  the  opening  is  cast  in 
cylindrical  moulds,  in  which  it  solidifies  and  becomes  roll  sulphur. 

Large  quantities  of  sulphur  are  also  obtained  by  distilling  iron 
pyrites,  a  compound  which  contains  iron  and  sulphur,  and  which 
gives  up  part  of  its  sulphur  when  it  is  heated. 

95.  PROPERTIES. — Sulphur  is  a  brittle,  lemon-yellow  solid, 
having  neither  taste  nor  odor.  It  is  a  bad  conductor  of  electricity 
and  heat :  a  piece  of  roll  sulphur  held  firmly  in  the  hand  produces 
a  curious  crackling  noise,  because  the  outside  becomes  warm,  and 
its  expansion  causes  it  to  crack  before  the  heat  can  be  conducted 
to  the  interior.  Sulphur  is  not  soluble  in  water,  is  very  slightly 
soluble  in  alcohol  and  ether,  but  dissolves  readily  in  carbon  disul- 
phide.  When  heated,  it  melts  at  111°,  and  becomes  a  mobile, 
brown,  and  transparent  liquid. 

We  melt  some  sulphur  in  an  earthen  crucible,  and,  as  soon  as  it 
has  all  melted,  we  allow  it  to  cool  until  a  crust  forms  over  the 
surface.  We  now  make  a  hole  in  the  crust,  and  pour  out  the  sul- 
phur which  has  not  solidified.  On  breaking  off  the  crust,  we  find 
the  interior  of  the  crucible  lined  with  beautiful,  transparent  crys- 
tals, which  on  close  examination  we  determine  to  be  oblique 
rhombic  prisms.  In  a  glass  flask  we  melt  some  more  sulphur,  but 
after  it  has  melted  we  keep  on  heating  it :  we  see  that  the  color 
becomes  darker,  and  the  liquid  thicker.  When  its  temperature 
reaches  220°,  we  can  turn  the  flask  upside  down  and  the  sulphur 
scarcely  runs  on  the  sides.  At  about  260°  it  again  becomes 
liquid,  and  as  soon  as  we  see  it  becoming  more  fluid,  we  pour  it 
into  a  vessel  of  cold  water,  moving  the  flask  so  that  all  does  not 
fall  in  the  same  place.  On  taking  the  sulphur  from  the  water, 
we  find  that  its  properties  are  much  changed :  it  is  transparent 
and  very  elastic ;  we  pull  it  out  in  long  threads.  This  curious 
form,  which  is  called  soft  sulphur,  is  due  to  a  molecular  condition 


SULPHIDES. — HYDROGEN    SULPHIDE.  75 

of  the  element ;  we  must  believe  that  its  molecules  contain  more 
en  :rgy  than  those  of  ordinary  sulphur,  for  if  we  gradually  heat  it, 
it  it  once  becomes  opaque  and  brittle,  and  at  the  same  time  much 
ho  ter  than  we  have  heated  it.  It  changes  spontaneously  in  this 
manner  after  we  have  kept  it  a  few  hours.  Soft  sulphur  is  amor- 
phous; that  is,  has  no  crystalline  form. 

Besides  these  two  forms  of  sulphur,  prismatic  crystals  and  soft 
su  phur,  there  is  another.  When  it  is  found  crystallized  in  nature, 
th  •  crystals  are  right  rhombic  octahedra.  After  a  time  the  crystals 
in  our  crucible  become  opaque  and  brittle :  when  we  examine 
tli  'm,  we  find  that  each  little  prism  has  separated  into  several 
oc  ahedra,  the  faces  of  which  hold  together  until  we  break  them 
aj.  irt. 

When  a  solution  of  sulphur  in  carbon  disulphide  is  evaporated, 
th  j  sulphur  is  deposited  in  the  octahedral  form,  and  at  ordinary 
to  uperatures  the  other  forms  gradually  change  to  this.  Because 
su  phur  has  more  than  one  distinct  physical  form,  it  is  said  to  be 
dinorphous.  The  density  of  prismatic  sulphur  is  1.98;  that  of 
oc  ahedral  sulphur  is  2.05. 

96.  Sulphur  takes  fire  in  the  air  at  a  temperature  below  red- 
ne?s:  its  combustion  is  its   union  with  oxygen,  forming  sulphur 
dioxide,  SO2,  called  also  sulphurous  oxide  and  sulphurous  acid 
ga^.      By  the  aid  of  heat,  sulphur  unites  directly  with  many  other 
elements  :  we  have  seen  in  one  of  our  experiments  (§  4)  that  cop- 
pe  •  burns  brilliantly  in  sulphur  vapor,  and  in  the  same  manner  we 
might  burn  some  iron  wire,  forming  iron  sulphide. 

Sulphur  is  used  in  the  manufacture  of  matches,  gunpowder, 
sulphuric  acid,  and  many  other  operations. 

97.  Sulphides. — We  put  a  little  antimony  sulphide  into  a  test- 
tube,  and  boil  it  with  some  hydrochloric  acid.     A  gas  having  the 
unpleasant  odor  of  rotten  eggs  is  given  off,  and  antimony  chloride 
remains  in  the  tube.    This  gas,  which  we  shall  now  study,  is  called 
hydrogen  sulphide,  or  sulphuretted  hydrogen  ;  nearly  all  the  sul- 
phides form  this  gas  when  boiled  with  hydrochloric  acid,  and  the 
reaction  gives  us  a  test  for  the  sulphides. 

98.  Hydrogen  Sulphide,  IPS.— Into  a  bottle  like  that  which 


76 


LESSONS    IN    CHEMISTRY. 


served  for  the  preparation  of  hydrogen,  we  put  some  ferrous  sul- 
phide, which  we  have  made  by  heating  to  redness  in  an  earthen 
crucible  a  mixture  of  iron  filings  with  about  its  own  weight  of 
sulphur.  We  then  pour  through  the  funnel-tube  some  dilute  sul- 
phuric acid,  and  at  once  or  in  a  few  minutes  an  effervescence  shows 
us  that  gas  is  being  given  off,  and  we  soon  detect  this  gas  by  its 
odor.  It  is  a  compound  of  hydrogen  and  sulphur,  and  is  formed 
by  the  reaction 

FeS  +         H2SO*       =  H2S  +  FeSO4 

Ferrous  sulphide.        Sulphuric  acid.        Hydrogen  sulphide.        Ferrous  sulphate. 

The  ferrous  sulphate  formed  remains  dissolved  in  the  water. 

As  we  often  desire  this  gas  in  the  laboratory,  we  sometimes 
employ  a  self-regulating  apparatus  consisting  of  two  bottles  which 

have  openings  near  the 
bottom,  and  these  open- 
ings are  connected  by  a 
stout  rubber  tube  (Fig. 
43).  In  one  we  put  a 
layer  of  clean  pebbles 
that  rise  above  the  lower 
opening,  and  on  this  the 
ferrous  sulphide ;  to  the 
neck  of  this  bottle  we 
adapt  a  glass  stop-cock  by 
the  aid  of  a  good  cork. 
In  the  other  bottle,  which 
we  must  not  cork,  we  pour  our  dilute  sulphuric  acid.  When  we 
open  the  stop-cock,  the  acid  runs  in  on  the  ferrous  sulphide ;  the 
gas  is  then  formed,  and  we  may  keep  it  in  the  bottle  or  use  it  as 
we  desire :  when  we  close  the  stop-cock,  the  gas  forming  in  the 
bottle  forces  the  acid  into  the  other  bottle,  and  as  soon  as  the  sur- 
face of  the  acid  is  below  the  top  of  the  layer  of  pebbles,  the  fer- 
rous sulphide  is  no  longer  acted  on.  We  may  use  this  apparatus 
for  the  preparation  of  hydrogen  and  carbon  dioxide  (§  234),  of 
course  cleaning  it  out  before  changing  the  materials. 

99.  PROPERTIES. — Hydrogen  sulphide  is  a  colorless  gas,  having 


FIG.  43. 


HYDROGEN    SULPHIDE.  77 

a  scinking  and  penetrating  odor.  Its  density  being  17  times  that 
of  hydrogen  or  17  X  .0693  that  of  the  air,  its  molecular  weight 
must  be  34  (§  48).  By  strong  pressure  it  is  converted  into  a  color- 
less liquid.  At  ordinary  temperatures  water  dissolves  about  three 
times  its  volume  of  hydrogen  sulphide,  and  the  solution  is  some- 
tin  es  used  in  the  laboratory,  but  it  does  not  keep  long,  for  the  air 
ox  dizes  the  hydrogen,  forming  water,  while  sulphur  is  deposited. 

Ve  can  easily  determine  the  composition  of  this  gas.  Into  a  long  test-tube 
of  lard  glass  we  thrust  a  roll  of  tin  foil,  and,  after  tightly  corking  the  tube, 
wo  heat  it  until  the  tin  acquires  a  yellow  color.  After  the  tube  has  cooled,  we 
un  ork  it  under  the  surface  of  mercury,  and  we  find  that  the  volume  of  gas 
ha  not  changed.  This  gas  is  hydrogen,  and  two  volumes  (one  molecule)  of 
hy  rogen  sulphide  therefore  contain  two  volumes  (two  atoms)  of  hydrogen. 
If  roin  the  density  (half  the  molecular  weight)  of  hydrogen  sulphide  we  sub- 
tni  -t  that  of  hydrogen,  we  obtain  (17  —  1  =  16)  a  number  equal  to  the  weight 
of  lalf  the  sulphur  in  a  molecule  of  the  compound.  The  sulphur  in  a  mole- 
cul  :  of  hydrogen  sulphide  therefore  weighs  32  if  the  hydrogen  weighs  2. 

Hydrogen  sulphide  is  a  combustible  gas,  as  we  can  easily  under- 
st;  ad,  since  its  molecule  contains  only  hydrogen  and  sulphur,  both 
of  which  are  able  to  unite  with  the  oxygen  of  the  air,  the  first  to 
foi  tn  water,  and  the  second  to  form  sulphur  dioxide,  the  same  gas 
wl  ich  is  formed  when  sulphur  burns  in  the  air.  When  we  light 
the  gas  at  the  end  of  the  delivery-tube,  it  burns  with  a  blue  flame. 

LOO.  Certain  reactions  of  this  gas  make  it  exceedingly  valuable 
in  the  laboratory.  We  pass  the  delivery-tube  from  our  apparatus 
into  a  solution  of  copper  sulphate  in  water :  a  brownish-black  pre- 
cipitate is  formed  as  soon  as  the  gas  comes  in  contact  with  the 
liquid.  This  is  copper  sulphide,  and  sulphuric  acid  remains  in  the 
solation. 

CuSO4        +        IPS  CuS  .  +  H2SO* 

Copper  sulphate.  Copper  sulphide.  Sulphuric  acid. 

We  pass  the  gas  into  a  solution  of  antimony  chloride,  and  an 
orange-colored  precipitate  of  antimony  sulphide  forms,  while  hydro- 
chloric acid  is  in  the  liquid. 

2SbCl3         +         3H2S  Sb2S3         +         6HC1 

Antimony  chloride.  Antimony  sulphide. 

In  a  solution  of  zinc  acetate,  we  would  have  thrown  down  a 
white  precipitate  of  zinc  sulphide.  Naturally,  in  these  reactions 


78  LESSONS    IN    CHEMISTRY. 

we  must  know  by  analysis  the  composition  of  the  molecules  which 
react  together,  and  that  of  the  bodies  which  are  formed,  before  we 
can  write  the  equations.  The  solutions  of  many  other  metallic 
compounds  are  decomposed  in  this  manner  by  hydrogen  sulphide, 
and  the  color  and  other  properties  of  the  metallic  sulphide  formed 
show  us  what  metal  exists  in  the  solution  to  which  we  apply  the 
test. 

Hydrogen  sulphide  is  at  once  decomposed  by  chlorine,  hydro- 
chloric acid  being  set  free. 

H2S  -I-  Cl2  =  2HC1  +  S 

Hydrogen  sulphide  is  a  poisonous  gas,  and  must  not  be  inhaled 
for  any  length  of  time,  even  when  very  much  diluted  with  air. 

101.  Sulphydrates. — We  have  seen  that  hydrates  are  formed  by  the  action 
of  water  on  the  oxides  (§  62),  and  that  these  hydrates  contain  the  group  of 
atoms  OH,  which  we  call  hydroxyl.  On  examining  the  composition  of  the 
molecule  of  hydrogen  sulphide,  we  see  that  it  is  exactly  like  that  of  water, 
but  contains  a  sulphur  atom  instead  of  an  oxygen  atom. 

HOH  HSH 

Water.  Hydrogen  sulphide. 

There  are  also  compounds  exactly  like  the  hydrates,  but  containing  sulphur 
instead  of  oxygen,  and  they  are  called  sulphydrates.  We  pass  hydrogen  sul- 
phide into  a  solution  of  potassium  hydrate ;  it  is  absorbed,  and  a  chemical 
reaction  which  takes  place  causes  the  liquid  to  become  warm. 

KOH  +  HSH  KSH  +    HOH 

Potassium  hydrate.  Hydrogen  sulphide.  Potassium  sulphydrate.  Water. 
We  cannot  fail  to  notice  the  similarity  between  the  structure  of  these  mole- 
cules, and  this  similarity  leads  us  to  the  conclusion  that  as  far  as  combining 
with  atoms  of  hydrogen  and  potassium  is  concerned,  there  must  be  a  resem- 
blance between  sulphur  atoms  and  oxygen  atoms.  We  will  in  time  notice  that 
this  resemblance  does  not  stop  here,  but  is  borne  out  in  the  structure  of  many 
other  molecules  containing  sulphur  and  oxygen  atoms.  Since  one  atom  of 
sulphur  or  one  of  oxygen  5s  capable  of  combining  with  two  atoms  of  hydrogen 
or  one  of  hydrogen  and  one  of  potassium,  and  since  we  take  the  hydrogen 
atom  as  the  unit  of  the  combining  power,  we  say  that  the  hydrogen  and 
potassium  atoms  are  mono-atomic,  and  that  the  oxygen  and  sulphur  atoms  in 
these  compounds  are  diatomic. 


SULPHUR    DIOXIDE.  79 

LESSON    XII. 
SULPHUR   DIOXIDE.— SULPHUR   TRIOXIDE. 

102.  Sulphur  Dioxide,  SO2. — This  compound  is  formed  when 
8i  Iphur  burns  in  the  air  or  in  oxygen :  we  could  not  obtain  it 
]>  ire  by  burning  sulphur  in  air,  for  it  would  then  be  mixed  with 
the  other  constituents  of  the  air.     We  usually  prepare  the  gas  by 
bailing  sulphuric  acid  with  copper  clippings:  the  products  of  the 
operation  are  cupric  sulphate,  water,  and  sulphur  dioxide:  know- 
it  g  this,  we  may  write  our  equation, 

Cu        +         2H2S04  CuSO4  +  2H20      +      SO2 

Copper.          Sulphuric  acid.        Cupric  sulphate.  Sulphur  dioxide. 

We  conduct  the  experiment  in  an  apparatus  like  that  in  which 
v  e  prepared  chlorine,  and  if  we  desire  to  collect  the  gas  we  do  so 
ly  downward  dry  displacement. 

103.  PROPERTIES. — Sulphur  dioxide  is  a  colorless,  suffocating 
gas.     Its  density  compared  to  hydrogen  is  32,  agreeing  with  that 
v  hich   our   theory  should  indicate  (§  48),  and  it  is  therefore  a 
little  more  than  twice  as  heavy  as  an  equal  volume  of  air.     By 
pressure,  or  by  a  temperature  of  — 10°,  it  is  converted  into  a 
colorless  liquid,  and  this  liquid  may  be  easily  prepared  by  passing 
the  gas  into  a  bottle  surrounded  by  a  mixture  of  ice  and  salt. 
The  evaporation  of  the  liquid  produces  great  cold :  a  temperature 
as  low  as  — 73°  has  been  obtained  by  aiding  this  evaporation  by 
pimps,  and  the  phenomenon  has  been  applied  in  the  construction 
of  certain  machines  for  making  ice.     We  can  easily  freeze  some 
water  in   a  test-tube  by  wrapping  the  lower  end  of  the  tube  in 
some  cotton  wool,  and  pouring  on  this  some  liquid  sulphurous 
oxide,  but  we  must  make  the  experiment  in  a  current  of  air  to 
carry  off  the  suffocating  gas. 

At  ordinary  temperatures  water  dissolves  about  forty  times  its 
volume  of  sulphurous  oxide,  and  the  solution  is  frequently  em- 
ployed in  the  laboratory. 


80  LESSONS    IN    CHEMISTRY. 

104.  Sulphurous  oxide  is  naturally  not  combustible,  for   the 
sulphur  which  it  contains  has  had   an   opportunity  to  combine 
with  all  of  the  oxygen   with  which  it  would  unite.     It  extin- 
guishes burning  bodies. 

While,  however,  one  atom  of  sulphur  will  not  combine  directly 
with  more  than  two^  atoms  of  oxygen,  sulphurous  oxide  can  be 
still  further  oxidized  by  certain  reactions.  If  it  be  mixed  with 
oxygen,  and  the  mixture  passed  through  a  red-hot  tube  containing 
platinum  sponge,  the  two  gases  combine,  forming  sulphur  trioxide, 
SO3 ;  the  vapor  of  this  substance  may  be  condensed  by  passing  it 
into  an  ice-cold  receiver.  By  the  action  of  nitric  acid,  sulphur 
dioxide  is  converted  into  sulphuric  acid,  and  the  reaction  is  applied 
in  the  manufacture  of  the  latter  acid. 

In  a  tall  jar  we  dissolve  some  potassium  permanganate  in  water ; 
this  body  contains  a  large  proportion  of  oxygen,  with  which  it 
parts  easily  to  oxidizable  matters.  We  pass  some  sulphur  dioxide 
through  the  purple  solution,  which  is  rapidly  decolorized;  the 
sulphur  dioxide  becomes  sulphuric  acid  in  this  reaction,  and 
the  potassium  permanganate  is  said  to  be  reduced.  We  use  the 
term  reduction  to  mean  taking  away  oxygen,  and  any  body  which 
is  capable  of  removing  oxygen  from  other  substances  is  called  a 
reducing  agent. 

Sulphur  dioxide  is  used  for  bleaching  wool,  straw,  and  other 
matters  which  would  be  injured  by  chlorine.  The  substances  are 
bleached  by  being  put  in  a  room  in  which  sulphur  is  burned.  We 
may  in  this  manner  bleach  a  flower  in  a  bell-jar  under  which  some 
sulphur  is  burning. 

105.  Sulphites. — When  sulphur  dioxide  dissolves  in  water,  the  two  sub- 
stances really  combine,  and,  by  a  reaction   analogous  to  that  which  formed 
hypochlorous  acid,  sulphurous  acid  is  formed.     In  this  case,  however,  the  two 
atoms  of  hydrogen  exist  in  one  molecule  of  the  resulting  acid. 

SO2  +        H20      =  H2S03 

Sulphur  dioxide.  Sulphurous  acid. 

Sulphurous  acid  is  not  a  stable  compound ;  it  is  decomposed  when  we  try  to 
separate  it  from  its  solution,  and  yields  again  sulphur  dioxide  and  water. 
However,  both  of  the  hydrogen  atoms  are  replaceable  by  metal,  forming  salts 
which  are  called  sulphites  ;  by  passing  sulphur  dioxide  into  a  solution  of  so- 
dium hydrate,  sodium  sulphite  and  water  are  formed. 


SULPHUR   TRIOXIDE.  81 

2NaOH          +         SO2  Na2S03         +         R2Q 

Sodium  hydrate.  Sodium  sulphite. 

To  a  little  of  this  sodium  sulphite  in  a  test-tube  we  add  hydrochloric  acid; 
we  3.in  at  once  detect  the  pungent  odor  of  sulphur  dioxide,  and  a  solution  of 
con  mon  salt  remains  in  the  tube. 

Na2S03  +  2HC1  -  SO2  +  H20  •;-  2NaCl 
Th  s  gives  us  a  test  by  which  we  may  recognize  a  sulphite. 

1  06.  When  a  sulphite  is  boiled  with  sulphur,  the  latter  is  dissolved,  and  a 
coi  ipound  called  a  thiosnlphate,  or  formerly  named  hyposulphite,  results. 
Wi:h  sodium  sulphite,  we  would  have  sodium  thiosulphate. 

Na2S03  +  S          =         Na2S203  or  Na2S03S 

Sodium  sulphite.  Sodium  tliiosulpliate. 

t  will  be  noticed  that  the  thiosulphate  has  exactly  the  composition  of  a 
sulohate  ($  113)  in  which  an  atom  of  oxygen  is  replaced  by  an  atom  of  sul- 
ph  ir.  When  a  thiosuiphate  is  treated  with  an  acid,  sulphur  dioxide  is 
ev  -Ived,  and  sulphur  separates.  The  rags  used  in  the  manufacture  of  paper 
ar  bleached  by  chlorine,  but.  no  chlorine  must  be  left  in  the  paper,  or  this 
w<  uld  be  injured.  In  presence  of  water,  sulphur  dioxide  (we  may  then  say 
su  phurous  acid)  and  chlorine  react  to  form  sulphuric  and  hydrochloric  acids, 
be  h  of  which  may  readily  be  neutralized. 

H'SO3         +        C12      +      H20  H2SO*         +        2HC1 

Sulphurous  acid.  Sulphuric  acid. 

S<  Hum  thiosulphate  therefore  serves  as  an  antichlor  in  the  manufacture  of 
p;  per. 

107.  Sulphur  Trioxide,  SO3. — We  have  seen  that  this  com- 
p<  und  is  formed  by  the  direct  union  of  sulphur  dioxide  and  oxy- 
gc  n  in  presence  of  heated  pladnum  sponge  (§  104)  :  other  porous 
substances  cause  the  same  combination.  Sulphur  trioxide  is  usu- 
al^ prepared  by  heating  fuming  sulphuric  acid,  which  is  some- 
times called  Nordhausen  acid,  because  it  was  for  a  time  manufac- 
tured only  in  the  village  of  Nordhausen,  in  Saxony,  by  distilling 
partially-dried  ferrous  sulphate.  It  is  a  compound  of  sulphur 
trioxide  and  sulphuric  acid  ;  H2S04  -f  SO3  =  IPS207.  When 
it  is  heated,  it  decomposes  into  its  constituents ;  the  sulphur  tri- 
oxide, being  the  most  volatile,  is  condensed  in  cold  flasks,  which 
are  at  once  hermetically  sealed. 

Sulphur  trioxide  is  a  snowy-white  solid,  crystallizing  in  feather- 
like  flakes.     It   combines  so  energetically  with  water  that  each 
particle  makes  a  hissing  noise  like  hot  iron  on  touching  the  liquid. 
The  result  of  this  combination  is  sulphuric  acid. 
SO3  +  H20  =  H2S04 


82  LESSONS    IN    CHEMISTRY. 

LESSON    XIII. 
SULPHURIC  ACID,  H2SO*. 

108.  Into  a  jar  of  oxygen  containing  a 'little  water,  we  lower  a 
deflagrating-spoon  containing  burning  sulphur.  The  jar  soon  be- 
comes filled  with  sulphur  dioxide,  and  when  the  flame  of  the  sul- 
phur is  extinguished,  we  pour  into  the  jar  a  little  nitric  acid.  Red 
vapors  at  once  become  apparent,  but  disappear  in  a  little  while : 
in  order  to  mix  the  gases  well,  we  now  shake  the  jar,  keeping  it 
closely  covered,  and  then  by  means  of  a  long  glass  tube  we  blow 
some  air  into  it :  red  vapors  are  again  produced.  It  is  evident 
that  some  chemical  change  has  occurred  between  the  nitric  acid 
and  sulphur  dioxide,  and  that  another  change  takes  place  between 
the  gases  in  the  jar  and  the  air  which  we  have  introduced.  The 
first  change  is  the  production  of  sulphuric  acid,  and  the  conversion 
of  the  nitric  acid  into  the  red  vapors  of  nitrogen  peroxide.  Since 
one  molecule  of  nitric  acid  contains  only  one  atom  of  hydrogen, 
while  one  molecule  of  sulphuric  acid  contains  two  such  atoms,  two 
molecules  of  nitric  acid  must  react  with  one  of  sulphur  dioxide. 

SO2  +     2HN03     =        H2SO*        +         2N02 

Nitric  acid.        Sulphuric  acid.          Red  vapors. 

The  red  vapors  react  with  the  water  in  the  jar,  and  again  yield 
nitric  acid  and  another  gas,  nitrogen  dioxide,  which  is  colorless. 

3N02       +  H20  =      2HN03      +  NO 

Red  vapors.  Nitric  acid.        .  Nitrogen  dioxide. 

The  nitric  acid  so  regenerated  oxidizes  more  sulphur  dioxide, 
and  this  reaction  continues  until  the  gases  in  the  jar  are  a  mixture 
of  nitrogen  dioxide  and  sulphur  dioxide.  But  the  nitrogen  diox- 
ide is  not  lost :  it  takes  an  atom  of  oxygen  from  the  air  blown  into 
the  jar,  and  again  forms  red  vapors. 

NO  +  0  =  NO2 

These  red  vapors  in  turn  react  with  the  water,  again  forming 
nitric  acid,  which  oxidizes  more  sulphur  dioxide,  and  this  series 


SULPHURIC    ACID.  83 

of  reactions  continues  until  all  of  the  sulphur  dioxide  is  converted 
into  sulphuric  acid. 

1 09.  These  reactions  are  those  which  actually  take  place  in  the 
manufacture  of  sulphuric  acid,  which  is  commonly  called  oil  of 
vitriol,  and  of  which  enormous  quantities  are  used  at  one  stage  or 
another  in  the   manufacture  of  nearly  all  other  chemical  com- 
poi  nds.     The  sulphur  dioxide  is  obtained  by  burning  sulphur  in 
fur  mces  (A A,  Fig.  44),  the  heat  of  which  boils  water  for  the 
ste  m  required  in  the  operation.      The  sulphur  dioxide  formed 
pu.-ses  through  a  series  of  leaden  chambers,  in  one  of  which  (D) 
it  (  oines  in  contact  with  nitric  acid,  which  trickles  down  over  a 
soi  ;  of  cascade  (EE).     The  gases  then  pass  through  other  leaden 
ch;  mbers  into  which  steam  is  injected  (HH)  for  the  regeneration 
of  nitric  acid,  and  the  sulphuric  acid  formed  collects  on  the  floor 
of  the  chambers,  from  which  it  is  drawn  off.     An  excess  of  air 
mi  st  be  passed  into  the  chambers  in  order  to  reoxidize  the  nitro- 
ge  t  dioxide,  and  as  the  nitrogen  of  the  air  which  must  be  allowed 
to  3scape  from  the  apparatus  would  carry  off  some  of  that  oxide 
of  nitrogen,  all   the  waste   gases  are  obliged  to  pass  through  a 
tover  (R)  filled  with  coke  which  is  kept  wet  with  strong  sulphuric 
acii.     This  latter  absorbs  the  nitrous  gases,  and  as  it  runs  from 
tht    tower  is  conducted  into  a  vessel  (i),  from  which  it  may  be 
foiled  by  steam  pressure  to  the  top  of  the  first  small  chamber  (C),' 
thiough  which  the  sulphur  dioxide  is  caused  to  pass.     Here  the 
sulphur  dioxide  removes  all  of  the  nitrous  gases  and  carries  them 
again  into  the  chambers,  so  that  only  nitrogen  from  the  air  used 
escapes  at  the  chimney  of  the  coke  column.     The  chambers  are 
of  various  sizes,  sometimes  five  metres  wide  and  high,  and  ten, 
twenty,  or  even  more  metres  in  length. 

The  acid  drawn  from  the  leaden  chambers  is  called  chamber 
acid:  it  is  strong  enough  for  many  purposes,  its  density  being 
1.5.  The  strong  acid,  density  1.842,  is  made  by  evaporating 
the  chamber  acid  in  leaden  boilers  until  its  further  concentration 
would  dissolve  the  lead ;  it  is  then  transferred  to  expensive  plati- 
num stills,  where  the  evaporation  is  terminated. 

110.  The  sulphuric  acid  of  commerce  always  contains  a  little 


84 


LESSONS    IN    CHEMISTRY. 


SULPHURIC   ACID.  85 

lend  sulphate,  formed  in  the  chambers  and  evaporating  boilers, 
an  1  when  it  is  diluted  with  water  this  lead  sulphate  becomes  in- 
soluble and  separates  as  a  white  precipitate.  It  is  often  brown 
frc  m  the  presence  of  a  little  carbonaceous  matter.  Sometimes  the 
su  phur  dioxide  is  obtained  by  burning  iron  pyrites  (iron  disul- 
pl  ide),  and,  as  the  pyrites  often  contains  arsenic,  the  resulting  sul- 
pl  uric  acid  also  contains  arsenic.  Pure  sulphuric  acid  is  made 
b\  distilling  the  commercial  acid  in  glass  retorts ;  the  operation 
re  [uires  great  care,  for  the  retorts  sometimes  break,  and  the  vapors 
of  the  sulphuric  acid  are  most  corrosive  and  suffocating. 

111.  Properties. — Pure  sulphuric  acid  is  a  colorless,  oily  liquid, 
h:  ving  at  12°  a  density  of  1.842.  It  solidifies  at  10.5°,  and  boils 
at  about  338°  :  its  boiling  is  accompanied  by  explosive  emission  of 
v«  por,  which  may  be  obviated  by  putting  some  pieces  of  platinum 
iu  the  vessel.  Sulphuric  acid  is  soluble  in  all  proportions  of  water, 
ai  d  the  mixture  is  accompanied  by  the  production  of  great  heat, 
si  owing  that  there  is  a  true  chemical  combination  between  the 
w  iter  and  acid.  In  diluting  sulphuric  acid  with  water,  we  always 
p-  ur  the  acid  very  gradually  into  the  water,  which  we  stir  con- 
st intly.  If  the  mixture  is  made  suddenly,  part  of  the  acid  is 
sc  rnetimes  thrown  out  of  the  vessel. 

The  affinity  of  sulphuric  acid  for  water  is  so  strong,  that  the 
acid  causes  the  formation  of  water  in  many  substances  which  do 
m  t  contain  water,  but  contain  hydrogen  and  oxygen  in  the  pro- 
portions required  for  its  formation.  In  a  beaker  glass,  or  other 
thin  glass  vessel,  we  pour  a  little  strong  solution  of  sugar,  and 
then  some  concentrated  sulphuric  acid  :  instantly  the  mixture  turns 
black,  and  a  mass  of  porous  charcoal  fills  the  vessel,  which  may 
overflow  if  we  have  used  too  much  of  the  materials.  Sugar  con- 
ta-ns  carbon  or  charcoal,  and  oxygen  and  hydrogen  in  the  propor- 
tions to  form  water.  For  the  same  reason  a  chip  of  wood  with 
which  we  stir  some  sulphuric  acid  quickly  becomes  blackened,  and 
the  brown  color  which  the  acid  acquires  shows  us  why  the  common 
acid  is  often  brown. 

When  sulphuric  acid  is  passed  through  a  red-hot  tube,  it  is 
decomposed  into  sulphur  dioxide,  oxygen,  and  water. 


86  LESSONS    IN   CHEMISTRY. 

R2SO*        =        SO2        +        0        +        H20 

We  have  already  seen  how  zinc  acts  on  sulphuric  acid,  replacing 
the  hydrogen  which  then  becomes  free.  The  action  of  copper  on 
the  acid  is  a  reducing  action,  part  of  the  sulphuric  acid  being 
reduced  to  sulphur  dioxide. 

112.  Molecular  structure  of  sulphuric  acid.  —  We  have  seen  that  hypochlorous 
acid  contains  the  group  hydroxyl,  OH;  sulphuric  acid  also  contains  this  group, 
and  we  may  understand  the  structure  of  its  molecule  by  studying  some  simple 
reactions.  Since  a  molecule  of  sulphur  dioxide  contains  two  atoms  of  oxygen, 
each  of  which  is  diatomic,  —  that  is,  capable  of  combining  with  two  atoms  of 
hydrogen,  —  the  sulphur  atom  must  in  this  compound  have  as  much  combining 
power  as  four  atoms  of  hydrogen  :  we  call  it  tetratomic.  Yet  this  sulphur  atom 
is  capable  of  combining  with  another  atom  of  oxygen;  it  is  unsaturated  with 
oxygen,  although  it  is  satisfied  with  the  two  atoms.  We  mix  in  a  glass  jar 
equal  volumes  of  chlorine  and  sulphur  dioxide,  and  expose  the  mixture  to 
direct  sunlight:  the  gases  combine  to  form  a  colorless  liquid,  having  a  suffo- 
cating vapor,  and  we  call  the  compound  sulphuryl  chloride.  Analysis  shows 
that  it  contains  S02C12,  and  for  convenience'  sake  the  group  of  atoms  SO2  is 
called  sulphuryl.  Each  atom  of  chlorine  is  worth  one  of  hydrogen,  and  if 
in  sulphur  dioxide  the  sulphur  atom  is  tetratomic,  it  must  be  hexatomic  in 
sulphury  1  chloride.  We  may  represent  this  relative  combining  capacity  by 
little  lines,  which  will  show  us,  not  how  and  where  the  atoms  unite,  but  the 
relative  worth  of  the  atoms  in  combination.  The  free  atom  of  hydrogen  or 
of  chlorine  would  be  indicated  to  be  monatomic  by  a  single  line,  thus,  H-,  C1-; 
and  in  the  molecules  of  these  two  elements  or  of  their  one  compound  a  single 
line  between  the  two  symbols  would  show  that  one  has  as  much  combining 
power  as  the  other  : 

H-H  C1-C1  H-C1 

The  symbol  of  a  diatomic  element  must  have  two  lines,  to  show  that  it  is 
worth  two  monatomic  atoms,  and  we  may  write  water  and  hydrogen  sulphide, 

H-O-H  H-S-H 

For  sulphur  dioxide,  sulphur  trioxide,  and  sulphuryl  chloride,  in  the  first 
of  which  the  sulphur  atom  is  tetratomic  and  in  the  other  two  hexatomic,  we 
must  show  the  combining  power,  or  atomicity,  as  it  is  often  called,  of  the 
elements  by  four  or  six  lines,  and  show  that  the  oxygen  is  diatomic  by  giving 
its  atoms  each  two  lines.  We  therefore  write, 
0=8=0 


ci 

Sulphur  dioxide.  Sulphuryl  chloride.  Sulphur  trioxide. 

When  sulphuryl  chloride  is  poured  into  water,  both  substances  are  decom- 
posed, sulphuric  and  hydrochloric  acids  being  formed. 

S02C12        +        2H*0  =  H2SO*        +        2HC1 


SULPHATES.  87 

\\  e  must  explain  this  reaction  by  a  replacement  of  the  chlorine  atoms  in  the 
PI  Iphuryl  chloride  by  other  atoms,  or  groups  of  atoms,  which  have  the  same 
ct  mbining  power,  and  we  would  then  conclude  that  sulphuric  acid  contains 
tvo  hydroxyl  groups,  and  we  might  call  it  sulphury  I  hydrate. 

0  0 

,'1-S-C1     +     II-O-H     +     H-O-H     :       H-0-S-O-H     +     HC1     +     HC1 

6  0 

S   Iphuryl  Water  (two  molecules).  Sulphuric  acid.          Hydrochloric  acid 

•  iloride.  (2  molecules.) 

Analogous  study  of  the  manner  in  which  compounds  are  formed  and  decom- 
}>  >sed,  and  of  the  relative  worth  of  the  atoms,  has  led  chemists  to  hold  definite 
ii  eas  of  the  relations  which  the  atoms  bear  to  each  other  in  a  great  number 

0  molecules.     The  group  of  atoms  OH  is  called  a  compound  radical  because  it 

1  capable  of  replacing  an  atom  or  simple  radical.     In  the  same  manner  the 
<r  'oup  SO2  is  a  radical,  as  in  general  are  all  groups  of  atoms  which  pass  by 
d  mble  decomposition  and  without  change  from  one  molecule  to  another.   Some 
i    dicals,  like  SO2,  can  be  separated  and  studied,  because  the  combining  power 
o    the  atoms  in  them,  though  not  saturated,  is  satisfied ;  others,  like  -OH,  can- 
i!  »t  be  separated,  because  their  atoms  are  not  satisfied  with  each  other.     Why 
t   is  is,  chemists  have  not  yet  been  able  to  explain  satisfactorily,  but  the  fact 
n  ay  be  stated  that  a  monatomic  radical  cannot  usually  exist  except  in  com- 
b  nation  :  this  applies  to  rnonatomic  atoms  as  well  as  to  monatomic  compound 
r  dicals ;  we  have  already  seen  that  the  molecules  of  hydrogen  and  chlorine 
D  ust  each  contain  two  atoms. 

There  are  two  other  elements  whose  atoms  exactly  resemble  sulphur  in  their 
p  >wer  of  combining  with  other  atoms.  They  are  selenium  and  tellurium. 
They  are  found  only  in  small  quantities,  usually  associated  with  gold  and 
silver  ores. 


LESSON    XIV. 
SULPHATES. 

113.  When  the  hydrogen  of  sulphuric  acid  is  replaced  by 
metals,  sulphates  are  formed,  but  as  there  are  two  atoms  of  hydro- 
gen, and  either  one  or  both  may  be  replaced,  we  can  understand 
that  there  may  be  two  kinds  of  sulphates.  If  only  one  hydrogen 
atom  be  replaced,  the  resulting  salt  will  have  acid  properties,  for 
it  still  contains  an  atom  of  replaceable  hydrogen  ;  but  if  both  be 
replaced,  we  have  a  neutral  salt, — that  is,  one  which  is  neither  acid 


88  LESSONS    IN   CHEMISTRY. 

nor  alkaline.  We  may  study  the  formation  of  two  of  these  salts 
in  the  reaction  of  one  and  two  molecules  of  sodium  hydrate  with 
one  molecule  of  sulphuric  acid. 

H2SO*      +       NaOH         =         NaHSO*         +         IPO 
Sodium  hydrate.        Sodium  acid  sulphate. 

H2S04      +      2NaOH         =         Na2S04         +         2H20 
Sodium  sulphate. 

But  in  the  action  of  zinc  on  sulphuric  acid,  one  atom  of  zinc 
replaces  two  atoms  of  hydrogen.  In  the  same  manner,  if  we  boil 
sulphuric  acid  with  lead  oxide,  we  have  formed  lead  sulphate,  in 
which  one  atom  of  lead  replaces  both  atoms  of  hydrogen. 

PbO        +        H2SO*        =        PbSO*        +        H20 
Lead  oxide.  Lead  sulphate. 

Since  one  atom  of  zinc  or  one  of  lead  is  thus  capable  of  replacing 
two  atoms  of  hydrogen,  those  metals  are  said  to  be  diatomic ;  and 
since  sulphuric  acid  contains  two  atoms  of  hydrogen  which  may  be 
replaced  by  two  atoms  of  a  monatomic  metal,  like  sodium,  or  by  one 
atom  of  a  diatomic  metal,  like  zinc,  it  is  called  a  dibasic  acid,  and 
is  capable  of  forming  neutral  and  acid  salts. 

114.  With  the  exception  of  the  sulphates  of  barium,  strontium, 
and  lead,  all  of  the  sulphates  are  soluble  in  water,  but  calcium 
sulphate,  silver  sulphate,  and  mercurous  sulphate  are  only  slightly 
soluble. 

115.  To  a  solution  of  magnesium  sulphate  we  add  a  few  drops 
of  solution  of  barium  chloride  or  barium  nitrate.     A  white  cloud 
forms ;  this  is  insoluble  barium  sulphate ;  when  it  has  settled,  we 
may  pour  off  most  of  the  liquid,  and  we  will  find  that  our  white 
substance  is  not  dissolved  by  boiling  nitric  acid.    This  test  enables 
us  to  recognize  either  a  soluble  sulphate  or  uncombined  sulphuric 
acid. 

Some  of  the  sulphates  form  anhydrous  crystals, — that  is,  with- 
out water;  others  require  water  of  crystallization. 

116.  Sodium  Sulphate,  Na2SO*,  was  for  a  long  time  called 
Glauber's  salt,  because  Glauber  found  that  it  was  useful  as  a  pur- 
gative medicine.     It  crystallizes  from  water  in  colorless,  rhombic 
prisms  containing  ten  molecules  of  water  of  crystallization,  so  that 


SULPHATES.  89 

tl  e  formula  of  the  crystals  is  Na2S04  -f-  10H20.  They  are  sol- 
uble in  about  ten  times  their  weight  of  water  at  0°,  and  in  one- 
tl  ird  their  weight  at  33°  ;  if  a  saturated  solution  be  made  at  the 
huter  temperature  and  immediately  sealed,  it  will  remain  liquid 
ii  definitely,  but  on  opening  the  flask  the  whole  of  the  liquid  in- 
st  intly  becomes  a  mass  of  crystals. 

117.  Potassium  Sulphate,   K2S04.  forms  very  hard,  colorless 
ci  ystals,  not  very  soluble  in  water ;  it  is  poisonous. 

118.  Calcium  Sulphate,  CaSO4.— We  have  in  a  beaker  glass  a 
v  ry  strong  solution  of  calcium  chloride.     To  this  we  add  at  arm's 
1(  igth  about  half  its  volume  of  concentrated  sulphuric  acid  :  the 
Ci  ntents  of  the  beaker  at  once  become  so  salid  that  we  can  in- 
v  rt  it  and  nothing  runs  out.     This  solid  is  calcium  sulphate. 

Cad2         +         H2SO*  CaSO*         +         2HC1 

Calcium  chloride.  Calcium  sulphate. 

Calcium  sulphate  is  the  mineral  gypsum,  alabaster,  or  selenite. 
I  i  these  minerals  it  is  combined  with  two  molecules  of  water  of 
ci  ystallization  ;  this  water  is  driven  out  when  they  are  heated  to 
1  !0°,  leaving  the  anhydrous  sulphate  as  a  fine  white  powder, 
k.iown  as  plaster  of  Paris.  Unless  it  has  been  heated  to  too  high 
a  temperature,  this  substance  will  again  combine  with  its  water  of 
crystallization,  and  such  combination  takes  place  when  plaster  of 
P  iris  is  mixed  with  water.  Plaster  casts  are  made  by  mixing  the 
pi  ister  and  water  to  a  creamy  consistence,  and  pouring  the  liquid 
in:o  the  moulds:  in  a  few  minutes  the  plaster  sets,  or  becomes 
hardened,  and  in  so  doing  it  expands  and  completely  fills  the 
mould.  Calcium  sulphate  dissolves  in  about  500  times  its  weight 
of  water.  It  is  a  valuable  fertilizer  for  certain  soils. 

119.  Strontium  Sulphate,  SrSO4,  constitutes  the  mineral  celes- 
tine,  so  called  because  it  often  has  a  blue  color,  though  the  pure  salt 
is  white.    It  is  insoluble  in  water,  and  is  precipitated  when  a  soluble 
strontium  salt  is  added  to  sulphuric  acid  or  a  soluble  sulphate. 

120.  Barium  Sulphate,  BaSO4,  is  found  native  as  heavy  spar. 
We  have  seen  that  it  is  formed  by  the  reaction  of  sulphuric  acid 
with  soluble  salts  of  barium.    It  is  sometimes  used  for  adulterating 
white  lead  (§  250). 


90  LESSONS    IN   CHEMISTRY. 

121.  Magnesium  Sulphate,  MgSO4  +  7H20,  is  commonly 
known  as  Epsom  salts.     It  is  made  by  dissolving  magnesium  car- 
bonate in  dilute  sulphuric  acid,  and  when  the  concentrated  solu- 
tion is  allowed  to  evaporate,  the  salt  separates  in  crystals  containing 
seven  molecules  of  water.     It  has  a  salty,  bitter,  and  unpleasant 
taste.     It  dissolves  in  about  three  times  its  weight  of  water.    It  is 
used  in  medicine. 

122.  Zinc  Sulphate,   ZnSO4  -f  7H20.— We  evaporate  to    a 
small  volume  the  liquid  remaining  in  the  bottle  in  which  we  made 
hydrogen  by  the  action  of  sulphuric  acid  on  zinc,  and  then  set  it 
aside  in  a  cool  place.      After  a  time  zinc  sulphate  separates  in 
beautiful  transparent  crystals,  containing  seven  molecules  of  water, 
and  of  exactly  the  same  form  as  those  of  magnesium  sulphate 
prepared  in  the  same  manner.     Compounds  which  have  in  their 
molecules  the  same  number  of  atoms  arranged  in  the  same  man- 
ner, usually  crystallize  in  the  same  form,  and  are  said  to  be  iso- 
morphous.     Zinc  sulphate  is  sometimes  called  white  vitriol.     It 
is  quite  soluble  in  water,  and  when  swallowed  it  acts  as  a  violent 
emetic. 

123.  Ferrous  Sulphate,  FeSO4  +  7H20.— This  salt,  called 
also  green   vitriol  and  copperas,  is  made  by  treating  scrap  iron 
with  dilute  sulphuric  acid ;  hydrogen  is  disengaged,  just  as  in  the 
action  of  the  same  acid  on  zinc.     When  the  filtered  solution  is 
evaporated  and  set  aside  to  crystallize,  the  ferrous  sulphate  sepa- 
rates in  crystals  which,  as  the  formula  would  indicate,  are  isomor- 
phous  with  the  two  preceding  salts.    These  crystals  are  pale  green 
in  color ;  when  exposed  to  dry  air,  they  lose  part  of  their  water 
of  crystallization,  and  the  surface  becomes  covered  with  a  white 
powder,  which  is  the  anhydrous  salt ;  they  are  said  to  effloresce. 
After  a  time  this  powder  becomes  yellow,  from  an  absorption  of 
oxygen  (§  527).    Ferrous  sulphate  is  soluble  in  less  than  twice  its 
weight  of  cold  water,  and  much  more  soluble  in  boiling  water. 
It  is  poisonous. 

124.  Cupric  Sulphate,  CuSO4  -f  5H20.— This  beautiful  blue 
salt,  often    called   blue  vitriol,  may  be  prepared  from  the  res- 
idue of  the  preparation  of  sulphur  dioxide  by  diluting  it  with 


NITROGEN. — THE    ATMOSPHERE.  91 

\\ater,  filtering,  and  evaporating  to  crystallization.  It  is  usually 
made  by  roasting — that  is,  heating  in  the  air — copper  sulphide 
(}  484),  and  treating  the  mass  with  water.  When  the  blue  crys- 
tals are  heated,  the  water  is  driven  out,  and  the  white  anhydrous 
s  dt  is  left.  Cupric  sulphate  dissolves  in  four  times  its  weight  of 
old,  or  twice  its  weight  of  boiling  water.  To  a  solution  of  this 
p  lit  we  add  a  little  ammonia  water ;  a  pale-blue  precipitate  forms, 
I  ut  when  we  add  more  ammonia  this  precipitate  again  dissolves, 
;  nd  a  deep-blue  liquid  is  obtained.  This  liquid  contains  ammo- 
i  iacal  cupric  sulphate.  Cupric  sulphate  is  used  in  telegraphic 
1  atteries,  in  dyeing,  for  electrotyping,  and  in  many  other  opera- 
tions.%  It  is  poisonous. 

125.  Lead  Sulphate,  PbSO4.— When  sulphuric  acid  or  the 
i oluticfn  of  a  sulphate  is  added  to  a  solution  containing  a  lead  salt, 
]  ?ad  sulphate  separates  as  a  white  precipitate.  It  occurs  in  nature 
j  s  the  mineral  anglesite.  It  is  insoluble  in  water,  but  dissolves 
i.i  strong  acids. 

Of  the  many  other  sulphates,  we  must  study  a  few  when  we 
:•  ball  have  learned  some  of  the  peculiarities  of  the  corresponding 
i  letals. 


LESSON    XV. 
NITROGEN.-THE   ATMOSPHERE. 

126.  Nitrogen,  N  —  14. — On  the  water  in  the  pneumatic 
trough,  we  float  a  small  capsule  containing  a  little  sand  on  which 
v/e  have  placed  a  piece  of  phosphorus.  We  ignite  the  phos- 
phorus, and  place  over  it  a  bell-jar  which  may  rest  on  the  shelf 
in  the  trough  (Fig.  45).  At  first,  as  the  heat  of  the  burning 
phosphorus  expands  the  air,  a  few  bubbles  of  air  escape  under  the 
edge  of  the  jar,  but  this  soon  stops;  presently  the  water  begins 
to  rise  in  the  jar,  and  the  phosphorus  no  longer  burns.  All 
the  oxygen  of  the  air  in  the  jar  has  been  consumed  by  the  phos- 
phorus, and  there  is  left  only  nitrogen,  with  which  in  the  free 


92 


LESSONS    IN    CHEMISTRY. 


FIG.  45. 


state  the  oxygen  was  mixed,  and  phosphoric  oxide.  The  latter 
will  presently  dissolve  in  the  water,  and  we  may  then  examine 
the  nitrogen. 

To  obtain  nitrogen  from. the  air,  it  is  only  necessary  to  remove 
the  oxygen.  When  we  wish  a  consider- 
able quantity  of  pure  nitrogen,  we  force  a 
current  of  air  through  a  tube  containing 
pieces  of  solid  potassium  hydrate,  which 
absorbs  the  moisture  and  carbon  dioxide, 
and  from  this  through  a  long  tube  con- 
taining red-hot  copper.  The  copper  com- 
i  bines  with  all  of  the  oxygen,  forming  cu- 
E  pric  oxide,  and  pure  nitrogen  passes  out 
at  the  end  of  the  tube. 

127.  Nitrogen  is  a  colorless,  tasteless, 
and  odorless  gas.     Its  density  compared 

to  air  is  0.97,  or  compared  to  hydrogen,  14  ;  as  its  atomic  weight 
is  also  14,  its  molecule  must  contain  two  atoms.  It  is  almost 
insoluble  in  water.  It  is  not  combustible,  neither  will  it  support 
the  combustion  of  other  substances.  It  combines  directly  with 
only  a  few  of  the  elements,  and  energy  is  absorbed  during  the 
formation  of  many  of  its  compounds ;  that  is,  the  nitrogen  atoms 
have  a  stronger  affinity  for  one  another  than  for  the  other  atoms 
with  which  they  are  combined. 

Before  considering  any  of  these  compounds,  we  must  study 
the'  composition  of  the  atmosphere  from  which  the  nitrogen  is 
derived. 

128.  The  Atmosphere, — The  chemical  composition  of  the  air 
was  first  determined  with  tolerable  accuracy  by  the  great  French 
chemist,  Lavoisier.  We  may  satisfy  ourselves  of  this  composition 
in  a  very  simple  manner.  Around  a  long  glass  tube,  closed  at 
one  end,  we  have  placed  four  caoutchouc  bands,  dividing  it  into 
five  equal  portions,  Into  this  tube,  which  must  be  perfectly  dry, 
we  drop  a  dry  piece  of  phosphorus,  and  tightly  cork  the  open 
end.  By  gently  heating  the  bottom  of  the  tube  over  a  lamp,  we 
inflame  the  phosphorus,  and  then  by  quickly  turning  the  tube 


THE    ATMOSPHERE. 


93 


bottom  up  and  giving  with  the  corked  end  a  few  sharp  blows  on 
the  table,  we  cause  the  burning  phosphorus  to  fall  the  whole 
length  of  the  tube.  If  our  experiment  has  been  well  made,  all 
the  oxygen  has  been  burned  from  the  air  in  the  tube,  which  we 
allnw  to  cool,  and  then  carefully  uncork  with 
tin  mouth  under  water.  As  soon  as  the  cork 
is  Irawn,  the  water  rises  to  the  first  division 
(F.g.  46).  The  air  which  we  have  roughly 
an  .lyzed,  then,  contained  about  one-fifth  oxy- 
ge  i  and  four-fifths  nitrogen  by  volume. 

L29.  A  very  accurate  analysis  of  air  is 
m;  de  by  the  aid  of  the  eudiometer,  which  we 
ha  re  studied.  Into  the  eudiometer  with  the 
ca<  utchouc  tube  and  plain  glass  tube,  which 
so  ved  for  the  synthesis  of  water  (§  42),  but 
wi  hout  the  enclosing  wide  glass  tube,  we  in- 
tr<  duce  100  measures  of  air  and  100  meas- 
ur  s  of  pure  hydrogen.  After  adjusting  the 
mi  rcury  level  in  the  two  tubes,  we  pass  an 
elc  3tric  spark :  at  once  the  oxygen  and  part 
of  the  hydrogen  are  converted  into  water, 
wl  ich  condenses,  and  the  volume  of  gas  is  re- 
du  ;ed.  We  know  that  water  is  formed  by  the  union  of  two 
volumes  of  hydrogen  and  one  volume  of  oxygen  ;  consequently 
onii-third  of  the  diminution  in  volume  must  be  caused  by  the 
renoval  of  the  oxygen  of  the  100  measures  of  air.  On  again 
adjusting  the  level  of  the  mercury,  we  find  that  instead  of  200 
measures  we  have  only  137.21.  The  oxygen  present  in  100 

200  —  137.21 

measures  or  air  must,  then,  have  been    -      — ,  or  ZU.yrf 

o 

measures.     We  conclude,  therefore,  that  100  volumes  of  air  con- 
tain 20.93  volumes  of  oxygen  and  79.07  volumes  of  nitrogen. 

130.  Since  oxygen  is  heavier  than  nitrogen,  these  relative  vol- 
umes will  not  express  the  relations  by  weight.  We  can  calculate 
tin.  weights  from  the  volumes,  and  the  result  would  show  us  that 
76.87  parts  by  weight  of  nitrogen  are  mixed  with  23.13  parts  of 


FIG.  46. 


94  LESSONS    IN    CHEMISTRY. 

oxygen.  These  proportions  are  confirmed  by  the  direct  analysis, 
which  is  made  by  passing  air  through  a  series  of  tubes  in  which 
all  traces  of  everything  but  oxygen  and  nitrogen  are  absorbed : 
thus  purified,  the  air  passes  through  a  tube  containing  red-hot 
copper  (§  127),  and  the  increase  in  weight  of  this  tube  gives  the 
amount  of  oxygen  in  the  air  analyzed.  The  nitrogen  passes  on  into 
a  glass  globe  in  which  a  vacuum  has  previously  been  made,  and 
of  course  the  increased  weight  of  this  globe  is  the  amount  of 
nitrogen. 

The  air  is  not  a  compound,  but  a  mixture,  and  we  may  expect 
that  the  proportions  of  the  constituents  shall  vary  a  little.  How- 
ever, the  composition  is  about  constant :  hundreds  of  analyses 
have  shown  that  the  proportion  of  oxygen  in  100  volumes  of 
unconfined  air  varies  only  from  20.9  to  21.  Over  large  surfaces 
of  water,  as  on  the  open  sea,  there  is  a  little  less  oxygen  (20.6), 
because  that  gas  is  more  soluble  in  water  than  is  the  nitrogen. 

131.  We  pour  into  a  plate  some  perfectly  clear  lime-water;  in 
a  few  minutes  a  thin,  white  pellicle  forms  over  its  surface.     This 
pellicle  is  calcium  carbonate,  and  has  been  formed  by  the  absorp- 
tion of  carbon  dioxide  from  the  air.     Air  also  contains  more  or 
less  vapor  of  water,  which  is  deposited  in  the  form  of  dew  on  very 
cold  objects. 

The  proportions  of  vapor  of  water  and  carbon  dioxide  may  be  determined 
by  drawing  a  known  volume  of  air  through  a  series  of  tubes  (Fig.  47),  the 
first  of  which  contain  pumice-stone  and  sulphuric  acid,  and  the  others  frag- 
ments of  potassium  hydrate.  The  sulphuric  acid  absorbs  the  vapor  of  water, 
and  the  increase  in  weight  of  the  first  tubes  (D,  E,  F)  gives  the  weight  of  that 
vapor.  The  carbon  dioxide  is  absorbed  by  the  potassium  hydrate,  and  the 
increase  in  weight  of  the  tubes  containing  it  (A,  B,  C)  gives  us  the  proportion 
of  that  gas.  The  volume  of  air  which  contained  these  quantities  of  carbon 
dioxide  and  watery  vapor  is  equal  to  the  volume  of  water  which  runs  from  the 
aspirator  (V),  the  air  passing  through  the  tubes  and  into  the  aspirator  to  take 
the  place  of  the  water  running  out.  We  can  calculate  the  weight  of  this  air 
from  its  volume,  for  at  0°  and  under  760  millimetres  barometric  pressure, one 
litre  of  dry  air  weighs  1.2932  grammes. 

132.  The  quantity  of  vapor  of  water  which  the  air  can  take 
up  depends  on  the  temperature,  and   air  is  said  to  be  saturated 
with  moisture  when  at  the  given  temperature  it  can  hold  no  more 


THE    ATMOSPHERE. 


95 


water  vapor.  It  is  then  said  to  have  a  relative  humidity  of  100 : 
at  the  same  temperature  half  that  quantity  of  vapor  would  be  a 
relr.tive  humidity  of  50.  But  if  the  temperature  be  increased 


FIG.  47. 

and  the  quantity  of  moisture  remain  the  same,  the  relative  hu- 
mi  lity  is  lowered,  for  the  air  is  then  capable  of  dissolving  more 
vapor.  The  temperature  at  which  air  is  completely  saturated  with 
vapor  is  called  the  dew-point,  and  this  may  be  determined  by  noting 
the  temperature  at  which  moisture  begins  to  deposit  on  the  walls 
of  u  vessel  which  is  artificially  cooled. 

Substances  which  are  capable  of  absorbing  the  moisture  from 
the  atmosphere  are  said  to  be  hygroscopic.  By  reason  of  its  affinity 
for  water,  sulphuric  acid  placed  in  an  open  vessel  will  in  a  few  days 
absorb  from  the  air  enough  moisture  to  double  its  volume. 

133.  Carbonic  acid  gas  is  present  in  the  air  in  only  small  pro- 
portions ;  from  four  to  six  parts  in  ten  thousand  parts  of  air.  It 
is  thrown  into  the  atmosphere  from  volcanoes,  fissures  in  the  earth, 
and  mineral  springs,  but  the  largest  quantity  is  produced  by  com- 
bustion and  respiration.  It  does  not  accumulate  in  the  atmosphere, 


96 


LESSONS    IN   CHEMISTRY. 


but  is  absorbed  by  plants,  and  under  the  influence  of  sunlight  is 
decomposed,  the  carbon  being  retained  for  the  growth  of  the  plant, 
while  oxygen  is  eliminated.  If  we  put  some  ten- 
der leaves,  water  cress  answers  very  well,  in  ajar 
which  we  fill  with  water  at  the  pneumatic  trough, 
and  place  on  a  plate  so  that  the  water  may  not  run 
out,  and  then  expose  to  direct  sunlight,  in  a  short 
time  bubbles  of  gas  collect  in  the  jar  (Fig.  48). 
We  may  transfer  this  gas  to  a  small  tube,  and  if 
we  test  it  by  a  lighted  match,  we  find  that  it  is 
oxygen.  We  can  prove  that  carbon  dioxide  ex- 
ists in  the  air  exhaled  from  the  lungs,  by  blowing  the  breath  through 
lime-water  (Fig.  49),  which  quickly  becomes  clouded  by  the  for- 
mation of  calcium  carbonate.  In  the  same  manner,  if  we  burn  a 

lighted  taper  or  candle  in  a 
covered  jar,  and  then  pour  in 
some  lime-water,  and  shake 
the  jar,  the  milkiness  of  the 
water  shows  that  carbon  di- 
oxide has  been  formed. 

134.  Although  in  uncon- 
fined  air,  plants  and  vegetables 
remove  the  carbon  dioxide,  so 
that  its  proportion  does  not 
increase,  yet  if  the  air  be  con- 
fined, as  in  a  room  or  a  mine, 
this  gas  may  accumulate  to  as 
much  as  one  part  in  a  hundred 
of  air.  As  this  carbon  dioxide 
is  formed  at  the  expense  of 

the  oxygen  of  the  air,  the  proportion  of  oxygen  may  descend  as 
low  as  22  parts  per  hundred  by  weight,  instead  of  23.13.  A 
single  gas-burner  burning  about  160  litres  of  gas  per  hour,  con- 
sumes the  oxygen  of  about  240  litres  of  air,  and  produces  about 
130  litres  of  carbon  dioxide.  At  every  breath,  a  man  consumes 
about  4.87  per  cent,  of  the  oxygen  which  he  inhales,  and  the 


FIG.  49. 


AMMONIA. 


97 


carbon  dioxide  exhaled  in  an  hour  is  about  20  litres.  When  the 
carbon  dioxide  in  the  air  is  pure,  its  proportion  may  be  much 
increased,  and  no  ill  effects  result ;  but  in  addition  to  this  gas  a 
considerable  proportion  of  animal  matters  passes  from  the  lungs, 
and,  together  with  that  thrown  off  in  the  perspiration,  quickly 
vituites  the  atmosphere  of  an  apartment  which  is  not  ventilated. 
Gc>  >d  ventilation  requires  from  six  to  ten  thousand  litres  of  air  per 
hoi  r  for  each  individual.  In  dwellings  and  workshops,  most  of 
the  ventilation  is  by  the  cracks  of  doors  and  windows.  Fires  in 
op<  n  grates  afford  excellent  ventilation,  the  draught  of  the  chimney 
drawing  a  constant  supply  of  air  into  the  room. 

35.  Besides  the  substances  already  considered,  air  always  con- 
tai  is  very  small  quantities  of  ammonia,  traces  of  nitric  acid,  and 
sm  11  solid  particles  of  various  natures  which  are  carried  to  great 
dis  ances  by  the  winds.  Sometimes  a  little  ozone  is  present,  and 
ma  {  be  recognized  by  the  test  which  we  have  studied  (§  66). 


LESSON    XVI. 
AMMONIA  AND   ITS   COMPOUNDS. 

]36.  Ammonia,  NH3. — In  a  glass  flask  to  which  we  have 
adapted    a    cork    and 
delivery-tube,   we  mix 
son  e  powdered  ammo 
mum  chloride  with  its 
own    weight    of    pow- 
dered quick-lime.     We 
then  fill  the  rest  of  the 
flask    with    pieces    of 
lime,   and   gently  heat 
it  on  a  sand-bath.     We 
soon  notice  the  pungent 
odor  of  the  gas  disen- 
gaged ;  as  this  gas  is  very  soluble  iu  water,  we  cannot  collect  it 
E       ff  9 


FIG.  50. 


98 


LESSONS    IN   CHEMISTRY. 


over  that  liquid ;  we  may  collect  it  either  over  mercury  in  a  small 
pneumatic  trough,  or  by  upward  dry  displacement,  for  it  is  lighter 
than  air  (Fig.  50).  Quick-lime  is  calcium  oxide,  CaO  ;  ammo- 
nium chloride  is  a  compound  of  nitrogen,  hydrogen,  and  chlorine, 
NH4C1.  We  may  write  the  reaction, 

2NH*C1          +          CaO      =      2NR3      +        CaCl?          +        IPO 
Ammonium  chloride.  Lime.  Ammonia.        Calcium  chloride. 

The  calcium  chloride  formed  remains  in  the  flask,  and  the 
water  is  absorbed  by  the  pieces  of  lime  which  we  have  put  into 
the  flask  for  that  purpose.  We  could  not  dry  ammonia  gas  by 
passing  it  over  either  calcium  chloride  or  sulphuric  acid,  for  it 
combines  with  both  of  those  substances. 

137.  Properties. — The  ammonia  which  we  have  collected  is  a 
colorless  gas,  having  a  penetrating,  pungent  odor,  and  a  burning 
taste.  We  must  not  inhale  too  much  of  it,  for,  although  not 
poisonous,  it  often  produces  sudden  giddiness  or  vertigo.  Its 
density  compared  to  hydrogen  corresponds  with  half  its  molecular 

weight,  being  8.50 :  it  is  therefore  a 
little  more  than  half  as  heavy  as  air. 
By  strong  pressure,  it  is  readily  con- 
verted into  a  liquid,  and  this  liquid 
is  employed  in  some  forms  of  ice- 
machines,  where  it  produces  great  cold 
by  its  evaporation. 

Ammonia  is  very  soluble  in  water : 
at  0°  water  will  dissolve  1000  times 
its  volume  of  the  gas,  and  at  ordinary 
temperatures  about  700  times  its  vol- 
ume. We  have  fitted  to  a  glass  flask 
a  cork  through  which  passes  a  tube 
drawn  out  to  a  small  opening  on  the 
inside.  We  fill  this  flask  with  am- 
inonia,  by  dry  displacement,  and  after 
putting  in  the  cork  we  dip  the  end  of 

the  tube  into  a  vessel  of  water.     The  water  slowly  rises  in  the 
tube,  but  as  soon  as  it  reaches  the  narrow  end  the  ammonia  is 


AMMONIA    AND    ITS    COMPOUNDS. 


99 


absorbed  so  rapidly  that  the  pressure  of  the  atmosphere  forces  the 
water  up  in  a  fountain  which  continues  until  all  of  the  ammonia 
is  lissolved.  (Fig.  51.)  The  solution  of  ammonia  in  water  is 
called  ammonia- water,  or,  more  commonly,  spirits  of  hartshorn. 
It  has  the  taste  and  odor  of  the  gas,  and  is  very  caustic.  When  it 
is  heated,  the  gas  is  driven  out,  and  we  may  most  readily  obtain 
an  monia  by  heating  strong  ammonia-water  in  a  flask,  and  drying 
th  -  gas  by  passing  it  through  a  tube  containing  quick-lime.  The 
st]  jng  ammonia-water  of  commerce  contains  about  35  per  cent,  of 
th-j  gas.  Its  density  is  about  0.86. 

.'58.  Ammonia  is  decomposed  into  nitrogen  and  hydrogen  by  very  high 
tci  peratures  or  by  the  continued  passage  of  electric  sparks.  Two  volumes  of 
an  aionia  yield  four  volumes  of  the  mixed  gases,  and  if  we  mix  in  the  eudiom- 
et(  •  these  four  volumes  with  one  and  a  half  volumes  of  oxygen  and  pass  the 
sp;  rk,  after  the  condensation  of  the  water  formed,  only  one  volume  of  gas  is 
lei  .  This  is  nitrogen,  and  two  volumes,  or  one  molecule,  of  ammonia  must 
thi  refore  contain  one  volume  (one  atom)  of  nitrogen,  and  three  volumes  (three 
at<  ins)  of  hydrogen. 

139.  Ammonia  is  combustible,  but  it  will  not  burn  in  the  air. 
AY  3  may  cause  it  to  burn  at  a  jet  which  is  surrounded  by  oxygen, 
an  1  for  that  purpose  we  have  fitted  to  a 
sh  >rt  wide  tube,  open  at  both  ends,  a  cork 
tin  ough  which  pass  two  tubes  (Fig.  52)  ; 
on-j  of  them  is  short  and  leads  oxygen 
from  a  gas-holder,  while  the  other  reaches 
nearly  to  the  top  of  the  wide  tube,  and 
conveys  ammonia  gas  from  a  small  flask 
in  which  we  boil  some  ammonia-water. 
As  soon   as   ammonia-gas   escapes  from 
the;  jet,  we  turn  on  the  oxygen,  and  light 
the-  ammonia,  which  burns  with  a  yellow 
flame,  forming  water  and  nitrogen. 
4NH»  +  SO2  =  6H20  +  2N2 

This  combustion  may  be  made  to  take 
place  more  slowly,  and  in  an  interesting  manner,  in  the  presence 
of  platinum.  Over  some  ammonia-water  contained  in  a  beaker 
glass  (Fig.  53)  we  suspend  a  coil  of  red-hot  platinum  wire,  so 


FIG.  52. 


100 


LESSONS   IN    CHEMISTRY. 


FIG 


that  it  may  nearly  touch  the  liquid.  The  coil  will  continue  to 
glow  for  a  long  time  by  the  heat  evolved  from  the  slow  combustion 
of  the  ammonia  which  escapes  from  the  liquid 
and  mixes  with  the  oxygen  of  the  air.  If  now 
we  warm  the  beaker,  and  pass  bubbles  of  oxygen 
through  the  liquid,  each  bubble  causes  a  little 
explosion  as  it  combines  with  the  hydrogen  of 
the  ammonia.  Sometimes  the  beaker  becomes 
filled  with  white  fumes  of  a  compound  known 
as  ammonium  nitrite. 

140.  Ammonium  Compounds. — Ammonia  is  the  only  com- 
pound of  nitrogen  and  hydrogen  which  chemists  have  been  able 
to  prepare,  and  it  seems  that  one  atom  of  nitrogen  has  affinities 
for  only  three  atoms  of  hydrogen.  However,  that  same  atom 
may  combine  with  another  atom  of  hydrogen  if  certain  other  ele- 
ments be  present. 

Over  a  small  capsule  containing  some  warm  ammonia-water  we 
have  inverted  a  glass  jar,  and,  at  a  little  distance,  over  another  cap- 
sule in  which  is  some 
warm  hydrochloric 
acid  we  have  inverted 
another  jar.  Each 
jar  now  contains  some 
of  the  gas  from  the 
liquid  under  it.  When 
we  raise  the  jars  and 
^IG-  54-  bring  their  mouths  to- 

gether, both  become  filled  with  dense  white  fumes  (Fig.  54). 
The  two  gases  have  combined,  and  a  body  called  ammonium  chlo- 
ride has  been  formed,  and  will  settle  on  the  sides  of  the  jars.  The 
combination  is  very  simply  expressed. 

NH3  +  HC1  =  NH*C1,  ammonium  chloride. 

We  see,  then,  that  while  the  nitrogen  atom  will  combine  with 
only  three  atoms  of  hydrogen  alone,  it  will  combine  with  four  if 
an  atom  of  chlorine  come  with  that  hydrogen.  In  the  same  man- 
ner, in  many  other  compounds  one  nitrogen  atom  is  combined  with 


AMMONIUM 


101 


four  hydrogen  atoms,  and  one  other  atom  or  group  of  atoms.  NH4 
is  one  of  those  groups  of  atoms  which  we  call  radicals  (§  112)  ;  it 
passes  from  one  compound  to  another  without  change,  just  as  an 
atom  of  hydrogen  may  pass  from  one  molecule  to  another.  It 
caanot,  however,  be  separated  in  the  free  state  from  any  of  these 
compounds.  It  is  called  ammonium. 


LESSON    XVI  I. 
AMMONIUM   COMPOUNDS. 

141.  Ammonium  Chloride,  NH4C1. — This  compound  is  formed 
b;  the  direct  union  of  ammonia  and  hydrochloric  acid.  During  the 
nj  mufacture  of  illuminating  gas  by  the  distillation  of  coal,  more 
oi  less  ammonia  is  formed ;  it  must  be  removed  before  the  gas  is 
fi  for  use,  and  this  is  accomplished  by  washing  the  gas  with  water 
(^  225).  A  dilute  solution  of  ammonia  is  thus  obtained,  and  this 
is  the  source  of  the  ammonia  and  ammo- 
nium compounds  of  commerce.  For  the 
preparation  of  ammonium  chloride  this 
g<  s  liquor  is  heated  with  lime,  and  the 
ai  imonia  gas  given  off  is  passed  into 
hydrochloric  acid.  The  solution  is  then 
e\  aporated,  and  the  residue  of  ammonium 
cl  loride  is  purified  by  sublimation  in 
stoneware  pots.  It  may  be  formed  by 
another  and  interesting  reaction  :  we  pass 
into  a  jar  of  dry  chlorine  the  drawn-out 
erd  of  a  tube  through  which  ammonia  is 
escaping  ;  at  once  the  ammonia  takes  fire, 

being  partially  decomposed  with  production  of  hydrochloric  acid, 
which  at  once  unites  with  another  portion  of  the  ammonia,  forming 
white  clouds  of  ammonium  chloride  (Fig.  55). 

2NH3     -f     3C12     =     N2     +     6HC1 

6HC1     +     6NH3     =  :     6NH4.C1 

9* 


102,  t  i  ^  t^  :  V  ^ r-EsfiONS  IN^  CHEMISTRY. 

When  pure,  ammonium  chloride  is  in  translucid  masses,  which 
have  a  fibrous  structure,  and  are  quite  tough  and  difficult  to  pul- 
verize. It  dissolves  in  two  and  a  half  times  its  weight  of  cold 
water,  and  in  much  less  hot  water.  Its  taste  is  not  unpleasantly 
salty  and  sharp.  Unless  in  large  doses,  it  is  not  poisonous. 

142.  Ammonium  Sulphate,  (NH*)2SO*,  is  manufactured  by 
passing  into  dilute  sulphuric  acid  the  ammonia  which  is  disen- 
gaged when  gas  liquor  is  heated  with  lime.     It  is  in  white,  color- 
less crystals,  readily  soluble  in  water,  having  a  sharp  taste.     It 
may  be  used  for  the  manufacture  of  ammonia,  and  is  employed  as 
a  fertilizer. 

143.  Ammonium  Sulphydrate,  NH4.SH. — We  have  already 
noticed   the   composition   and   mode  of  formation   of  potassium 
sulphydrate  (§  101).     When  hydrogen  sulphide  is  passed   into 
ammonia-water  until  the  liquid  will  dissolve  no  more  of  the  gas, 
ammonium  sulphydrate  is  formed. 

NH»        +        HSH        =        NHiSH 

It  is  a  colorless  liquid,  but  becomes  yellow  after  it  has  been  for 
some  time  exposed  to  the  air.  Its  odor  is  disgusting,  being  at 
the  same  time  that  of  hydrogen  sulphide  and  that  of  ammonia. 
If  it  be  mixed  with  a  quantity  of  ammonia-water  exactly  equal  to 
that  from  which  it  was  prepared,  ammonium  sulphide  is  formed. 

NH*SH        +        NH3        =        NH4.S.NH4        =         (NH*)2S 

Ammonium  sulphide. 

This  compound  is  of  much  value  in  the  laboratory  in  detecting 
some  metals. 

To  a  solution  of  ferrous  sulphide  we  add  a  few  drops  of  ammo- 
nium sulphide,  and  a  black  precipitate  of  ferrous  sulphide  is  thrown 
down. 

NH*.S.NH4       +          FeSO*         =          (NH4)2SO*        +          FeS 
Ammonium  sulphide.      Ferrous  sulphate.        Ammonium  sulphate.      Ferrous  sulphide. 

We  pour  a  few  drops  of  the  same  liquid  into  a  solution  of  zinc 
sulphate,  and  white  zinc  sulphide  is  precipitated. 

(NH*)2S         +         ZnSO4        =         (NH*)2SO*         +         ZnS 

144.  On  examining  the  composition  of  the  ammonium  compounds,  we  see 
that  the  radical  NH4  has  the  same  combining  power  as  one  atom  of  hydrogen. 


AMMONIUM    AMALGAM. — NITROGEN    IODIDE.  103 

It  is  a  monatomic  radical;  but  at  the  same  time  we  notice  that  it  can  replace 
th  3  hydrogen  atoms  in  (he  acids,  and  in  so  doing  it  forms  salts.  It  is  a  basic 
i-udical,  and  is  in  this  respect  exactly  opposite  to  the  radicals  CIO-  and  SO2, 
which  are  acid  radicals. 

145.  Ammonium    Amalgam. — We    make    an    amalgam    of 
s<  dium, — that  is,  a  compound  of  sodium  and  mercury, — by  throw- 
ii  g  on  the  surface  of  a  little  mercury  a  few  small  pieces  of  sodium. 
I:   these  do  not  at  once  combine  with  the  mercury,  we  can  readily 
e1  ect  the  combination  by  touching  them  with  a  drop  of  water  on 
tl  e  end  of  a  long  glass  rod.     As  little  pieces  of  burning  sodium 
a  e  sometimes  thrown  out,  we  keep  the  vessel  at  a  sufficient  dis- 
t;  nee  from  the  eyes.     We  now  pour  this  amalgam  into  a  tall  jar 
Ci  ntaining  a  strong  solution  of  ammonium  chloride  :  at  once  a  very 
curious  phenomenon  occurs.     The  mercury  begins  to  swell  and 
1)  come  pasty ;  it  rises  and  floats  on  the  water,  and  sometimes  it 
o  erflows  the  jar;     On  pouring  it  out  and  examining  it,  we  find 
tl  at  it  has  become  a  brilliant,  butter-like  substance,  very  light,  and 
entirely  unlike  the  mercury.     In  the  reaction  which   has  taken 
p  ace,  the  sodium  has  left  the  mercury  and  combined'  with  the 
cl  lorine  of  the  ammonium  chloride.     The  ammonium  radicals  thus 
si  t  free  have  at  once  combined  with  the  mercury,  forming  this 
body  which  we  call  the  ammonium  amalgam. 

2NH*.C1  -f  HgNa2  2NaCl  +         NH*.Hg.NH* 

Ai  imonium  chloride.      Sodium  amalgam.      Sodium  chloride.        Ammonium  amalgam. 

Ammonium  amalgam  will  amalgamate  with  iron,  a  property 
w  lich  ordinary  mercury  does  not  possess.  It  does  not  keep  long, 
but  soon  decomposes  into  mercury,  ammonia  gas,  and  hydrogen. 

146.  Nitrogen  Iodide, — We  have  reduced  a  small  quantity  of 
iodine  to  a  fine  powder,  and  we  throw  this  into  a  little  ammonia- 
water.     Part  of  it  dissolves,  and  the  other  part  is  converted  into 
a  black   powder,  which  we  carefully  pour  on  a  small  filter  placed 
in  a  funnel.     When  most  of  the  liquid  has  drained  off,  we  dis- 
tribute this  powder  on  several  pieces  of  filter-paper,  which  we  set 
aside  for  the  powder  to  dry.     When  it  is  dry,  the  lightest  touch 
causes  it  to  explode  with  a  loud  noise,  and  sometimes  it  explodes 
spontaneously.     In  any  case  the  explosion  is  always  accompanied 
by  the  production  of  purple  vapors  of  iodine.     The  black  powder 


104  LESSONS    IN   CHEMISTRY. 

is  nitrogen  iodide :  there  are  several  such  compounds,  and  their 
composition  depends  on  the  exact  manner  of  formation ;  we  may 
express  it  by  NP.  It  is  formed  by  a  reaction  which  yields  also 
ammonium  iodide. 

4NH3      +     3I2      =          3NH4I  +  Nl3 

Ammonia.        Iodine.        Ammonium  iodide.        Nitrogen  iodide. 

The  ammonium  iodide  is  formed  with  a  considerable  produc- 
tion of  energy ;  but  the  liquid  does  not  become  warm,  for  all  this 
energy  is  transferred  to  the  nitrogen  and  iodine  atoms  which  com- 
bine to  form  nitrogen  iodide.  Where  must  we  seek  the  energy  of 
explosion  of  nitrogen  iodide  ?  The  explosion  is  only  a  rearrange- 
ment of  the  atoms ;  a  decomposition  of  the  nitrogen  iodide ;  the 
energy  of  this  decomposition  we  must  consider  as  the  energy  of 
formation  of  nitrogen  molecules  and  iodine  molecules,  of  which  the 
atoms  then  disengage  the  energy  conferred  on  them  by  the  forma- 
tion of  ammonium  iodide,  and  retained  in  the  nitrogen  iodide. 


LESSON    XVIII. 
OXIDES   OF  NITROGEN. 

147.  Nitrogen  Monoxide,  N20. — In  a  glass  flask  on  a  sand- 
bath,  we  heat  some  ammonium  nitrate,  a  white,  crystalline  sub- 
stance obtained  by  neutralizing  ammonia  with  nitric  acid.     Our 
flask  being  provided  with  a  delivery-tube,  we  may  collect  the  gas 
over  the  pneumatic  trough  (Fig.  56).     The  ammonium  nitrate  is 
entirely  decomposed  into  water  and  nitrogen  monoxide  sometimes 
called  nitrous  oxide. 

NH*N03         =  N20  +  2H2Q 

Ammonium  nitrate.        Nitrogen  monoxide. 

As  the  water  is  converted  into  steam  by  the  heat  required  for  the 
experiment,  when  we  desire  to  collect  the  gas  in  a  gas-bag  we  pass 
it  first  through  an  empty  bottle  in  which  the  steam  may  condense. 

148.  Nitrogen    monoxide  is  a  colorless   gas,  having  no  odor, 


NITROGEN    MONOXIDE. 


105 


but  a  sweet  taste.  Its  density  is  22  compared  to  hydrogen,  or 
l.")27  compared  to  air.  It  is  liquefied  by  great  pressure,  and 
considerable  quantities  are  so  liquefied  in  strong  iron  cylinders,  in 


FIG.  56. 

o'der  that  the  gas  may  be  transported  in  small  bulk  for  the  use 
[)•'  dentists.  At  ordinary  temperatures,  water  dissolves  about  its 
o  vn  volume  of  nitrogen  monoxide ;  for  this  reason  some  of  the 
g  is  is  always  lost  when  it  is  collected  over  water. 

Nitrogen  monoxide  is  decomposed  by  heat,  two  volumes  of  the 
gus  yielding  two  volumes  of  nitrogen  and  one  of  oxygen.  Since 
the  gaseous  mixture  contains  a  much  larger  proportion  of  oxygen 
than  does  the  air,  nitrogen  monoxide  should  support  combustion 
better  than  the  air.  An  experiment  will  show  us  that  it  does  ; 
we  put  into  a  jar  of  nitrogen  monoxide  gas  a  taper  bearing  only  a 
spark  of  fire,  and  this  spark,  decomposing  the  gas  surrounding  it, 
sots  free  sufficient  oxygen  to  relight  the  taper  (Fig.  57).  In  the 
same  manner  phosphorus  and  sulphur  burn  brilliantly  in  this  gas. 

Nitrogen  monoxide  is  not  poisonous ;  it  may  be  inhaled  for  a 
short  time  without  danger,  and  its  inhalation  is  followed  by  insen- 
sibility, a  condition  called  anaesthesia.  Advantage  is  taken  of  this 
property  of  the  gas  for  the  performance  of  short  surgical  oper- 


106 


LESSONS    IN    CHEMISTRY. 


ations.    The  first  effects  of  the  inhalation  of  the  gas  are  often  a 

condition  of  excitement  and  disposition  to  gayety ;  for  this  reason 

it  has  been  called  laughing-gas. 
149.  Nitrogen  Dioxide, 
NO. — In  a  gas-bottle,  provided 
with  a  delivery-tube  and  funnel- 
tube,  we  have  some  copper  clip- 
pings  and  water.  Through  the 
funnel-tube  we  pour  nitric  acid 
until  there  is  a  brisk  disengage- 
ment of  gas.  At  first  this  gas 
in  the  gas-bottle  is  red,  for 
reasons  which  we  shall  presently 
learn,  but  soon  it  becomes  almost 
colorless.  We  then  pass  the  de- 
livery-tube underwater,  and  col- 
lect the  gas  in  jars  filled  with 
FIG.  57.  water  (Fig.  58).  In  the  reaction 

which  is  taking  place,  the  copper 

is  replacing  the  hydrogen  of  the  nitric  acid,  and  every  atom  of 

copper  replaces  two  atoms  of  hydrogen. 


Cu 

Copper. 


2HN03 

Nitric  acid. 


Cu(N03)2 
Cupric  nitrate. 


2H 


But  in  this  case  the  hydrogen  is  not  set  free  ;  it  reduces  more 
nitric  acid,  and  if  we  keep  our  generating  bottle  cool  by  placing 
it  in  cold  water,  the  reduction  yields  NO  and  water.  As  the  cop- 
per atoms  always  set  free  even  numbers  of  hydrogen  atoms,  we 
cannot  write  this  reaction  3H  -f  HNO3  —  2  IPO  -f-  NO,  but 
must  write  6H  -f  2HN03  =  4H20  -j-  2NO  ;  and  since  the  six 
atoms  of  hydrogen  must  be  replaced  by  three  atoms  of  copper, 
each  of  which  requires  two  molecules  of  nitric  acid  besides  the 
two  that  are  reduced,  we  may  write  the  whole  equation 


3Cu 


8HN03    =     3Cu(N03)2 


4H20 


2NO 


While  this  gas  is  called  nitrogen  dioxide,  we  must  remember 
that  its  molecule   does  not  contain  two  atoms  of  oxygen  :    the 


NITRIC    OXIDE. 


107 


name  will  only  help  us  to  remember  that  it  is  the  second  oxide  of 
ni  rogen.     A  better  name  is  nitric  oxide. 

150.  Nitric  oxide  is  a  colorless  gas,  of  which  we  must*  remain 


ig  lorant  of  the  taste 
ai-d  odor,  for  it  forms 
a  corrosive  gas  as  soon 
as  it  is  exposed  to  the 
ai  •.  Its  density  com- 
p;  red  to  air  is  1.039. 
Ii  is  almost  insoluble 
in  water.  It  has  been 
Hi  _uefied  by  great  cold 
a  i  d  pressure. 

It  is  decomposed  by  / 


0 


h.  at,  but  not  so  readily  ^^ma^gi^ 


FIG.  58. 


F  >r    this    reason,    al- 

tl  ough  it  contains  in  a  given  volume  twice  the  proportion  of 
oxygen  in  nitrogen  monoxide,  it  will  not  relight  a  taper  bearing 
a  spark  :  it  will,  however,  support  the  combustion  of  phosphorus 
ard  charcoal. 

The  most  remarkable  property  of  nitric  oxide  is  its  affinity  for 
oxygen.  We  uncover  a  jar  filled  with  the  gas,  and  instantly  a 
cloud  of  red  vapor  is  formed.  This  is  the  red  gas  which  was 
formed  in  the  generating  bottle  when  the  nitric  oxide  first  elimi- 
nated came  in  contact  with  the  air  in  the  bottle.  In  this  experi- 
ment one  molecule  of  nitrogen  dioxide  takes  an  atom  of  oxygen 
from  the  air,  and  the  red  vapor  is  the  gas  NO2.  We  must  be 
careful  not  to  inhale  this  gas,  for  it  is  very  injurious. 

We  pour  a  few  drops  of  carbon  disulphide  into  a  jar  of  nitric 
oxide.  The  vapor  of  this  volatile  liquid  at  once  mixes  with  the 
gas,  and  when  we  apply  a  flame,  a  bright  flash  of  light  fills  the 
jar  as  the  carbon  is  burned  by  the  oxygen  of  the  nitric  oxide. 
The  light  produced  by  this  little  explosion  affords  an  excellent 
means  for  causing  the  direct  combination  of  hydrogen  and  chlorine 
(§  71). 


108 


LESSONS    IN    CHEMISTRY. 


We  pour  a  little  ferrous  sulphate  solution  into  a  jar  of  nitric 
oxide  ;  some  of  the  gas  is  at  once  absorbed,  and  the  liquid  becomes 
brown.  The  nitric  oxide  may  be  driven  out  by  heating  the  solu- 
tion, and  the  pure  gas  is  sometimes  prepared  in  this  manner. 

151.  In  nitric  oxide  the  affinities  of  the  nitrogen  atom  are  not  exhausted  :  we 
have  seen  that  it  is  still  able  to  combine  with  an  atom  of  oxygen.  It  will  also 
combine  with  an  atom  of  chlorine;  when  one  volume  of  chlorine  is  mixed 
with  two  volumes  of  nitric  oxide,  the  gases  unite,  forming  a  compound  NOCl. 
When  this  compound  is  treated  with  water,  both  substances  are  decomposed, 
yielding  hydrochloric  acid  and  nitrous  acid,  HNO2. 

NOCl     +     H20        =        HNO2     +     HC1 

Nitric  oxide  may,  then,  act  as  a  radical,  and  in  its  compounds  it  is  called 
nitrosyl.  NOCl  is  therefore  called  nitrosyl  chloride,  and  nitrous  acid  may  be 
called  nitrosyl  hydrate,  NO-OH. 


LESSON    XIX. 
OXIDES    OF  NITROGEN   (Continued). 

152.  Nitrogen  Peroxide,  NO2  and  N204. — We  may  form  this 
substance  by  the  direct  combination  of  nitric  oxide  and  pure  oxy- 
gen, and  we  would  of  course  require  two  volumes  of  the  first  and  one 
volume  of  the  second.  We  can  prepare  it  in  another  manner.  We 

heat  some  dry  lead  nitrate 
in  a  small  retort  placed  in 
a  sand-bath.  The  vapors 
given  off  are  conducted 
into  a  flask  surrounded  by 
ice  (Fig.  59).  Because  the 
lead  nitrate  cannot  well  be 
perfectly  dried,  we  change 
the  receiver  after  a  little 

plG  59  liquid  has  collected  in  it, 

and  throw  away  this  first 

portion.     That  which  now  collects  has  a  yellow  color,  and  if  we 
mix  a  little  salt  with  the  ice  around  the  receiver,  the  liquid  will 


NITROGEN    PEROXIDE.  109 

freeze  to  a  crystalline  mass.     The  lead  nitrate  is  decomposed  into 
lead  oxide,  oxygen,  and  nitrogen  peroxide. 

Pb(N03)2  PbO         +     0     +  N»0* 

Lead  nitrate.  Lead  oxide.  Nitrogen  peroxide. 

The  solid  nitrogen  peroxide  melts  at  — 10°  to  a  nearly  colorless 
li(,uid;  this  liquid  becomes  yellow  and  afterwards  orange-colored  as 
the  temperature  rises,  and  at  15°  is  red.  It  boils  at  22°,  giving 
tie  red  vapor,  and  the  density  of  this  vapor  compared  to  hydrogen 
is  46,  showing  that  the  molecular  weight  of  the  compound  is  92, 
ai  d  the  molecule  must,  therefore,  contain  N20*.  However,  as  the 
U  nperature  rises  the  density  diminishes,  and  at  70°  it  is  only 
01  e-half  46  ;  after  this,  the  density  remains  constant,  the  molecule 
h;  s  become  two  molecules,  and  each  of  these  must  contain  NO2. 
Such  decomposition  of  gases  by  heat  is  called  dissociation:  we  have 
al  eady  noticed  the  dissociation  of  water  vapor  (§  54)  and  nitrogen 
m  moxide. 

153.  Nitrogen  peroxide  dissolves  in  water,  but  in  dissolving  it 
re  icts  with  the  water ;  with  a  small  quantity  of  water  it  forms 
ni  rogen  trioxide  and  nitric  acid,  while  with  a  larger  quantity  it 
yi  slds  nitric  acid  and  nitrogen  dioxide. 

2N2O  +     IPO         =         2HN03         +  N203 

Nitrogen  peroxide.  Nitric  acid.  Nitrogen  trioxide. 

3N2Q4     +     2H20     =       4HX03     +     2ND 
With  the  alkaline  hydrates  it  yields  nitrates  and  nitrites. 

X204         +         2NnOH  NaNO3         +         NaNO2         +         H20 

Sodium  hydrate.         Sodium  nitrate.  Sodium  nitrite. 

A  similar  decomposition  really  takes  place  with  water,  but  the 
nitrous  acid  formed  is  at  once  decomposed  by  the  water. 

The  red  vapors  are  dangerous  to  inhale,  and  the  more  dangerous 
because  they  do  not  give  immediate  discomfort.  They  act  on  the 
delicate  membrane  of  the  lungs,  and  there  have  been  many  fatal 
accidents  where  the  gas  has  been  inhaled  by  workmen  repairing 
sulphuric  acid  chambers  (§§  108,  109). 

154.  Just  as  nitrogen  dioxide  may  act  as  a  radical  which  we  called  nitrosyl, 
nit.-ogen  peroxide,  NO2,  may  act  as  a  radical.  By  means  which  we  need  not 
consider,  chlorine  may  be  made  to  combine  with  nitrogen  peroxide,  and  the 
resulting  compound,  which  is  called  nitryl  chloride,  is  a  volatile  liquid  whose 

10 


LESSONS    IN    CHEMISTRY. 

molecule  is  expressed  by  the  formula  N02C1.  When  this  liquid  is  poured  into 
water,  nitric  acid  and  hydrochloric  acid  are  formed. 

N02C1     +     H20     =     HNO3     +     HC1 

We  may  therefore  regard  NO2  as  the  radical  of  N02C1  and  HNO3,  and  as  a 
radical  it  is  called  nitryl.  N02C1  is  then  nitryl  chloride,  and  nitric  acid  is 
in'tryl  hydrate,  N02.OH. 

155.  Nitrogen  Pentoxide,  N205.— When  vapor  of  nitryl  chloride  is  passed 
over  silver  nitrate,  heated  in  a  tube  to  70°,  the  silver  and  chlorine  atoms  leave 
their  respective  molecules  and  combine  together,  forming  silver  chloride;  the 
two  groups   of  atoms  from  which  the  chlorine  and  silver  are  removed  also 
combine  and  form  a  volatile  solid  compound  that  condenses  in  the  cooler  part 
of  the  tube.     This  body  is  nitrogen  pentoxide,  N205. 

N02-C1        +        AgO-NO2        =        AgCl        +         N02-0-N02 
Nitryl  chloride.  Silver  nitrate.  Silver  chloride.        Nitrogen  pentoxide. 

It  is  a  colorless  body,  melting  at  29.5°,  and  boiling  at  50°.  It  is  easily 
decomposed,  and  sometimes  explodes  spontaneously. 

156.  In  studying  the  other   elements   we   have  examined   the    combining 
powers  of  their  atoms,  compared  to  that  of  an  atom  of  hydrogen, — that  power 
to  which  the  name  atomicity  or  valence  (worth)  has  been  given.     What  is  the 
atomicity  of  the  nitrogen  atom  ?     The  molecule  of  nitrogen  monoxide  closely 
resembles  in  structure  the  molecule  of  water :  replace  by  two  atoms  of  nitro- 
gen the  two  atoms  of  hydrogen  of  water,  and  we  have  a  molecule  of  nitrogen 
monoxide.     The  nitrogen  atoms  here  have  the  same  combining  power  as  the 
hydrogen  atoms,  and  we  say  they  are  monatomic.     In  ammonia,  however,  the 
nitrogen  atom  itself  combines  with  three  atoms  of  hydrogen;  it  must  then  be 
worth  three  hydrogen  atoms,  and  we  call  it   triatoinic.     But  in  ammonium 
chloride  it  is  united  with  four  hydrogen  atoms  and  one  chlorine  atom;  since 
we  have  agreed  that  the  chlorine  atom  has  the  same  worth  as  the  hydrogen 
atom,  the  nitrogen  atom  in  ammonium   chloride  must  be  pentatomic.     Now 
let  us  look  at  the  other  oxygen  compounds  of  nitrogen  :  we  have  seen  that  in 
the  compounds  already  studied  the  oxygen  atom  is  diatomic,  and  indeed  we 
shall  in  time  find  that  there  are  many  reasons  for  believing  that  oxygen  is  al- 
ways diatomic.  Then  in  nitric  oxide,  NO,  the  nitrogen  atom,  which  is  combined 
with  only  one  oxygen  atom,  must  also  be  diatomic;  but  we  have  seen  that  this 
compound  NO  combines  directly  with  a  chlorine  atom,  forming  the  compound 
nitrosyl  chloride,  NO-C1  :  it  combines  with  a  hydroxyl  group,  which  is  mon- 
atomic, forming  nitrous  acid,  HO-NO,  and  in  these  compounds  the  nitrogen 
must  be  triatomic.     We  must  conclude,  however,  that  in   NO2  the  nitrogen  is 
tetratomic,  since  it  is  combined  with  two  atoms  of  diatomic  oxygen,  but  here 
again  an  atom  of  monatomic  chlorine  will  unite  with  the  nitrogen  atom  which 
is  then  pentatomic  in  nitryl  chloride,  N02C1.     At  low  temperatures,  when  the 
red  vapors  condense,  forming  molecules  of  N204,  it  seems  also  that  nitrogen 
is  pentatomic,  and  that  in  the  molecule  of  N20*  two  nitrogen  atoms,  each  of 
which  is  combined  with  two  oxygen  atoms,  are  also  cornbined  with  each  other. 


ATOMICITY    OF    NITROGEN.  Ill 

If  now  we  remember  our  representations  of  the  combining  powers  of  the 
atoms  by  short  lines,  we  may  see  how  the  atoms  in  these  molecules  seem  to  be 
rel  ited,  and  how  the  atomicity  of  nitrogen  varies. 

H  Cl 

N-O-N  H-N-H  N=0  C1-N=0  0=N=0 

Nitrogen  monoxide.     Ammonia.    Nitrogen  dioxide.    Nitrosyl  chloride.    Nitryl  chloride. 

'he  reactions  between  nitrosyl  chloride  and  water,  and  nitryl  chloride  and 
w:i  er,  then  become  double  decompositions  which  we  can  easily  understand. 


an  1  0-N-C1    +    H-O-H    -    0--N-0-H     +     H-C1 

Te  can  understand  also  how  nitrogen  peroxide  decomposes  by  the  action  of 
wa  er,  yielding  nitric  and  nitrous  acids. 

0±0     +     »-'-«     ^     °tH°       *     °™ 

Nitrogen  peroxide.        Water.         Nitric  acid.        Nitrous  acid. 

'hese  formula),  which  are  called  constitutional  or  graphic  formulae,  do  not 
in  my  manner  represent  the  positions  in  which  the  atoms  are  arranged;  they 
an  intended  to  show  what  atoms  are  in  relations  with  other  atoms  in  the 
UK  lecule.  We  must  believe  that  the  atoms  in  a  molecule  are  in  continual 
m<  Jon,  which  we  may  compare  to  the  motions  of  the  planets  around  the  sun, 
an  those  of  the  moons  around  each  particular  planet.  The  nature  of  the 
mo  ecule  depends  on  all  of  its  atoms,  just  as  the  nature  of  a  system  of  planets 
de]  ends  on  the  central  sun  and  all  the  planets  and  their  satellites;  and  just 
as  the  moon  would  go  with  the  earth  were  that  planet  to  be  withdrawn 
fro  11  the  solar  system,  so  do  certain  groups  of  atoms  enter  into  the  composition 
of  nolecules,  from  which  they  may  separate  as  groups  to  form  part  of  other 
mo  ecules  or  systems  of  atoms. 

Hereafter  we  shall  not  be  obliged  to  use  the  lines  to  represent  the  atomicity 
of  nil  the  atoms  in  the  molecules  of  which  we  study  the  structure.  We  know 
tha;  the  group  hydroxyl,  OH,  is  monatomic,  as  are  also  the  groups  NO  and 
NO2;  on  the  other  hand,  we  know  that  the  group  SO2  is  diatomic,  and  we 
can  represent  our  idea  that  each  of  these  groups  exists  in  the  molecule  as  a 
distinct  part  of  the  system  by  separating  it  from  the  rest  of  the  molecule  by  a 
period.  Thus  we  may  represent  nitric  acid  by  the  formula  NO2.  OH  :  sulphuric 
acin,  by  the  formula  S02.(OH)2. 


112 


LESSONS   IN    CHEMISTRY. 


LESSON    XX. 


NITRIC  ACID.     HNQ3. 

157.  Minute  quantities  of  nitric  acid  often  exist  in  the  atmos- 
phere, where  they  are  probably  formed  under  the  influence  of  at- 
mospheric electricity  on  the  nitrogen,  oxygen,  and  moisture  of  the 
air.     Wherever  organized  matters  containing  nitrogen  decompose 
in  the  presence  of  porous  substances  and  alkalies,  such  as  potas- 
sium hydrate,  sodium  hydrate,  or  lime,  nitrates  are  formed.     The 
nitric  acid  and  its  compounds  of  commerce  are  manufactured  from 
nitrates  which  are  found  abundantly  in  some  soils,  particularly  in 
India,  Egypt,  and  Chili :  in  the  latter  country  are  large  deposits 
of  sodium  nitrate. 

158.  We  may  prepare  some  nitric  acid  by  distilling  in  a  glass 


FIG.  60. 


retort  a  mixture  of  sodium  nitrate  and  sulphuric  acid,  and  con- 
densing the  vapor  in  a  flask  surrounded  by  cold  water.  On  the 
large  scale,  the  operation  is  conducted  in  cast-iron  retorts  (Fig. 
60),  and  the  vapor  is  condensed  in  a  series  of  large  stoneware 


NITRIC    ACID.  113 

b(  Ltles  which  are  called  bon-bons.  As  in  the  decomposition  of 
suiium  chloride  (§  75),  one  molecule  of  sulphuric  acid  may  be 
nude  to  decompose  either  one  or  two  molecules  of  either  potassium 
or  sodium  nitrate,  forming  at  the  same  time  either  a  neutral  or 
ai  acid  sulphate,  and  setting  free  one  or  two  molecules  of  nitric 
at  id. 

IPSO*     +         NaNO3  NaHSO*  +         HNO3 

Sodium  nitrate.  Sodium  acid  sulphate.  Nitric  acid. 

H2S04     +      2NaN03  Na2SO*  +         2HN03 


The  proportion  required  by  the  last  reaction  is  that  employed 
ii  the  arts,  as  it  is  more  economical.  Let  us  see  what  that  pro- 
p«  rtion  must  be  :  the  molecular  weight  of  sulphuric  acid  is 

°f  S°dium    nitmt<3   is  *     +        +      3  -  85' 


+  32  +  64 

T'ien   98  parts  of  sulphuric   acid,  and  85  of  sodium  nitrate,  if 
p.  rfectly  pure,  would  yield  ^  +  ^  f  ^  —  63  parts  of  nitric  acid. 

Properties,  —  Nitric  acid  is  a  colorless  liquid,  but  is  partially 
d»  composed  by  the  prolonged  action  of  light,  red  vapor  being 
firmed  and  communicating  a  yellow  color  to  the  acid  in  which 
it  dissolves.  It  is  very  volatile,  and  its  vapor  condenses  the 
m  >isture  in  the  air,  producing  white  fumes.  Its  density  is  1.5. 
It  freezes  at  —  49°,  and  boils  at  85°  ;  while  boiling  it  is  par- 
tially decomposed,  so  that  after  a  time  the  boiling  point  rises  to 
123°,  and  a  more  dilute  acid  distils,  having  the  same  strength  as 
th  it  left  in  the  retort.  It  mixes  with  water  in  all  proportions, 
airl  the  liquid  becomes  warm  during  the  mixture. 

159.  By  a  red  heat,  nitric  acid  is  at  once  decomposed  into 
water,  red  vapor,  and  oxygen,  a  decomposition  exactly  similar  to 
that  experienced  by  lead  nitrate  under  the.  action  of  heat  (§  152). 
2HN03  =  H2Q  +  2NO'2  +  0 

In  a  small  crucible,  or  a  thin  iron  dish,  we  heat  some  powdered 
charcoal  until  it  becomes  barely  red  hot.  We  now  remove  it  from 
the  fire,  and,  when  the  dish  has  cooled  a  little,  we  pour,  at  arm's 
length,  some  strong  nitric  acid  on  the  still  hot  charcoal.  At  once 
a  vivid  combustion  takes  place  ;  the  oxygen  of  the  decomposed 
k  10* 


114  LESSONS    IN    CHEMISTRY. 

nitric  acid  combines  with  the  carbon,  and  clouds  of  red  vapor  are 
given  off. 

On  the  end  of  a  stick  about  a  metre  long  we  tie  a  test-tube,  into 
which  we  pour  some  strong  nitric  acid,  and  if  our  nitric  acid  is 
not  the  strongest,  we  add  to  it  about  half  its  volume  of  sulphuric 
acid,  which  will  strengthen  the  nitric  acid  by  its  affinity  for  water. 
Then  in  another  iron  dish  we  carefully  warm  some  good  oil  of 
turpentine  until  it  is  nearly  boiling.  Now  we  warm  our  nitric 
acid,  and  standing  at  a  distance,  pour  it  suddenly  into  the  hot 
turpentine :  at  once  the  nitric  acid  oxidizes  the  turpentine,  and, 
unless  the  latter  has  previously  become  thick  by  too  long  exposure 
to  the  air,  it  will  be  inflamed. 

These  experiments  show  us  that  the  oxygen  atoms  have  not 
exhausted  their  energy  in  combining  with  nitrogen.  Indeed,  we 
have  seen  in  the  conversion  of  sulphur  dioxide  into  sulphuric  acid 
that  the  oxygen  of  nitric  acid  is  more  energetic  than  in  free  oxy- 
gen molecules  at  ordinary  temperatures,  for  we  have  to  heat  oxy- 
gen before  it  will  combine  with  sulphur  dioxide.  By  reason  of 
this  energy  still  existing  in  its  oxygen  atoms,  nitric  acid  is  easily 
reduced ;  that  is,  part  or  all  of  its  oxygen  may  be  readily  removed 
by  oxidizable  bodies.  We  have  seen  how  it  is  reduced  by  the 
hydrogen  of  another  portion  of  the  acid  when  copper  replaces  that 
hydrogen  (§  149)  :  in  this  same  reaction  part  of  the  nitric  acid  is 
converted  into  nitrogen  monoxide  and  even  free  nitrogen,  so  that 
the  nitric  oxide  prepared  by  nitric  acid  and  copper  is  never  per- 
fectly pure.  When  the  reduction  by  some  metals  is  carried  out 
to  its  full  limit,  the  nitrogen  combines  with  the  hydrogen,  forming 
ammonia.  This  occurs  in  the  action  of  zinc  on  very  dilute  nitric 
acid:  although  zinc  nitrate  is  then  formed,  no  hydrogen  is  set 
free,  for  the  displaced  hydrogen  reduces  the  nitric  acid  and  com- 
bines with  the  nitrogen  :  the  ammonia  formed  at  once  combines 
with  some  of  the  nitric  acid  present,  forming  ammonium  nitrate. 
HNO3  +  4H2  =  3H20  +  NH» 

160.  When  nitric  and  hydrochloric  acids  are  mixed,  a  liquid 
called  nitro-hydrochhric  acid,  or  aqua  regia,  is  obtained.  This 
liquid  is  capable  of  dissolving  gold  and  platinum,  a  power  pos- 


NITRIC    ACID.  115 

scssed  by  neither  of  the  separate  acids.  We  put  a  small  piece 
of  gold-leaf  in  a  test-tube  with  nitric  acid,  and  a  similar  piece 
in  another  tube  with  hydrochloric  acid.  In  neither  tube  is  the 
gold  affected,  but  on  mixing  the  liquids  both  pieces  are  dissolved. 
Nitro-hydrochloric  acid  converts  the  metals  into  chlorides,  the 
1)  drogen  of  the  hydrochloric  acid  reducing  the  nitric  acid,  and 
tl  e  chlorine  combining  with  the  metal. 

2HN03     +     2HC1     -     211*0     +     2NO*     +     Cl2 

161.  Nitrates. — When  the  hydrogen  of  nitric  acid  is  replaced 
by  metal,  nitrates  are  formed.     We  have  already  learned  that  an 
a  om  of  some  metals,  which  we  called  monatomic  metals,  is  capa- 
b  e  of  replacing  one  atom  of  hydrogen,  while  the  atoms  of  other 
n  etals  (diatomic)  are  able  to  replace  two.     Since  a  molecule  of 
n  trie  acid  contains  only  one  hydrogen  atom,  an  atom  of  zinc  or 
o  '  lead  must  replace  that  atom  in  two  molecules  of  nitric  acid,  and 
consequently  it  will  be  united  to  two  groups,  NO3.     Then,  while 
V*Q  can  express  the  molecules  of  potassium  and  sodium  nitrates  by 
tl  e  formulae  KNO3  and   NaNO3,  we  must  write  the  molecules  of 
had  and  zinc  nitrates  Pb(N03)2  and  Zu(N03)2. 

162.  Into  a  test-tube   containing  some  solution  of  potassium 
nitrate  in  water,  we  pour  a  little  solution  of  ferrous  sulphate,  and 
tl  en,  inclining  the  tube,  some  strong  sulphuric  acid.     This  last, 
being  much  heavier  than  the  other  liquids,  does  not  mix  at  once 
with   the  solution,  but  at  the  surface,  where  the  sulphuric  acid 
below  and  the  solution  of  the  nitrate  touch,  a  dark  ring  is  formed. 
This  is  caused  by  a  partial  reduction  of  the  nitric  acid  by  the  fer- 
rcus  sulphate,  which  produces  at  the  same  time  a  dark  color  with 
the  nitric  oxide  resulting  from  the  reduction.     This  color  disap- 
pears if  we  heat  the  tube  (§  150).    This  is  our  test  for  nitric  acid 
and  nitrates. 


116  LESSONS    IN    CHEMISTRY. 

LESSON    XXI. 
NITRATES. 

163.  All  of  the  nitrates  are  soluble  in  water.     Some  of  them 
form  anhydrous  crystals ;  others  require  water  of  crystallization. 
When  thrown  on  hot  coals,  they  decompose,  and  the  oxygen  given 
off  increases  the  intensity  of  the  combustion.     Salts  which  so  pro- 
mote combustion  are  said  to  deflagrate  on  hot  coals. 

164.  Sodium  Nitrate,  NaNO3,  is  found  in  large  quantities  in 
Chili  and  Peru.     It  forms  rhombohedral  crystals  that  are  almost 
cubical ;  it  is  very  soluble  in  water.     It  attracts  moisture  from 
the  air,  and  this  property  prevents  its  use  in  the  manufacture  of 
gunpowder  (see  §  166).     It  is  from  sodium  nitrate  that  nitric 
acid  and,  indirectly,  most  of  the  other  nitrates  are  prepared. 

165.  Potassium  Nitrate,  KNO3. — This  salt  is  commonly  called 
nitre  or  saltpetre.    In  some  hot  countries  it  forms  an  efflorescence, 
or  white  powder,  on  the  surface  of  the  soil,  and  may  be  obtained 
by  washing  the  soil  with  water  and  evaporating  the  resulting  solu- 
tion.    It  is  generally  made  by  a  double  decomposition  between 
the  sodium  nitrate  from  Chili  and  either  potassium   chloride  or 
potassium  carbonate.     Boiling  solutions  of  the  two  substances  are 
mixed,  and  the  sodium  chloride  or  carbonate  formed,  being  much 
less  soluble  in  boiling  water  than  the  potassium  nitrate,  may  be 
readily  separated. 

KCl  +        NaNO3  NaCl          -f  KNO3 

Potassium  chloride.        Sodium  nitrate.        Sodium  chloride.        Potassium  nitrate. 

K2C03  +        2NaN03       -  Na2C03          +          2KN03 

Potassium  carbonate.        Sodium  nitrate.        Sodium  carbonate.        Potassium  nitrate. 

Potassium  nitrate  forms  long,  six-sided  prisms  which  have  a 
bitter  and  cooling  taste.  They  dissolve  in  about  five  times  their 
weight  of  water  at  ordinary  temperatures,  but  require  less  than 
half  their  weight  of  boiling  water.  We  can  now  understand  how 
this  compound  may  be  separated  from  sodium  chloride,  which  is 


GUNPOWDER.  117 

about  equally  soluble  in  hot  and  cold  water  ;  for  when  a  boiling  satu- 
raied  solution  of  potassium  nitrate  is  cooled  to  ordinary  tempera- 
tures, nine-tenths  of  the  salt  separate  in  crystals,  but  from  a  boiling 
su'urated  solution  of  common  salt  very  little  is  deposited  on  cooling. 

Potassium  nitrate  "deflagrates — that  is,  increases  the  activity  of 
co  nbustion — when  thrown  on  hot  coals.  We  melt  some  zinc  in 
an  iron  ladle,  and,  when  it  is  nearly  red  hot,  we  throw  in  a  few 
su  all  pieces  of  potassium  nitrate  :  the  metal  takes  fire  and  burns 
in  o  zinc  oxide,  the  oxygen  being  supplied  from  the  decomposing 
pc  tassium  nitrate. 

1 66.  Gunpowder  is  a  mixture  of  about  seventy-five  parts  of  potas- 
sium nitrate,  ten  of  sulphur,  and  fifteen  of  charcoal.  It  is  made 
b\  grinding  each  substance  separately  to  the  finest  powder,  and 
th  in  mixing  them  and  grinding,  after  a  little  water  has  been  added. 
The  intimate  mixture  is  then  strongly  pressed  and  carefully  dried 
in  a  warm  room,  after  which  it  is  broken  into  grains  and  these  are 
silted  into  various  sizes.  The  grains  are  polished  by  friction  over 
ea  ;h  other  in  rotating  barrels.  This  mixture  contains  all  of  the 
materials  necessary  for  its  own  combustion,  and  the  result  of  the 
ex  plosion  may  be  generally  expressed  by  saying  that  the  sulphur 
co  nbines  with  the  potassium,  forming  potassium  sulphide,  while 
th-i  oxygen  of  the  nitre  unites  with  the  carbon  to  form  the  gases 
carbon  monoxide  and  carbon  dioxide,  which,  together  with  the 
nitrogen,  are  set  free.  The  gas  occupies  a  volume  very  much 
greater  than  that  of  the  powder  which  produced  it,  and  this  large 
volume  is  made  still  larger  by  the  high  temperature  of  the  reaction. 
Of  course  the  outside  of  the  grains  of  powder  must  burn  first,  and 
the  larger  the  grains  the  slower  the  combustion  and  the  consequent 
production  of  gas ;  but  the  smaller  the  grains  the  more  rapidly  is 
each  burned  and  the  flame  carried  from  one  to  the  other.  Hence 
the  small  quantity  of  powder  used  in  small-arms  is  in  fine  grains 
in  order  to  produce  instantly  as  much  force  as  possible ;  but  large 
guns  would  be  broken  by  such  sudden  strain,  and  large  grains  or 
lumps  are  employed,  which  are  put  into  the  gun  in  coarse  bags. 
In  blasting,  if  it  is  desired  to  break  the  rock  in  small  pieces,  a  very 
quickly  burning  powder  is  used ;  but  if  it  is  desired  to  split  off 


118  LESSONS    IN    CHEMISTRY. 

large  masses,  the  effect  is  accomplished  by  the  more  slowly  in- 
creasing pressure  from  a  slower  powder. 

167.  Silver  Nitrate,  AgNO3,  is  made  by  dissolving  silver  in 
nitric  acid,  and  evaporating  the  solution  until  it  crystallizes.     It 
forms  colorless  plates,  soluble  in  their  own  weight  of  water.     Its 
color  darkens  by  the  action  of  the  organic  matter  in  the  air  and 
exposure  to  light.    It  melts  when  cautiously  heated,  and  when  cast 
into  sticks  forms  the  lunar  caustic  used  by  surgeons.     It  is  a  cor- 
rosive body,  and  in  the  presence  of  moisture  destroys  the  tissues. 
Should  any  of  it  by  accident  be  swallowed,  common  salt  is  its  anti- 
dote ;  insoluble  silver  chloride  is  then  formed,  and  this  is  com- 
paratively harmless  (§  75).     When  silver  nitrate  is  highly  heated, 
it  leaves  a  residue  of  pure  silver. 

168.  Strontium   Nitrate,  Sr(N03)2.— This  salt  is  made  by 
dissolving  the  mineral  strontianite,  which  is  strontium  carbonate, 
in  nitric  acid,  and  purifying  by  several  crystallizations.     It  forms 
colorless  crystals,  quite  soluble  in  water. 

169.  Barium  Nitrate,  Ba(N03)2,  is  obtained  like  the  preceding 
salt,  but  withe-rite — barium  carbonate — is  used.    It  also  forms  color- 
less crystals,  soluble  in  water,  and  the  solution  may  be  used  as  a  test 
for  sulphuric  acid  (§  115). 

170.  Cupric  Nitrate,  Cu(N03)2  -f  3H20,  remains  in  the  bottle 
in  which  we  prepare  nitric  oxide.     If  we  filter  and  evaporate  this 
solution,  the  salt  separates  in  large  blue  prisms  ;  it  is  very  corrosive. 
When  strongly  heated,  it  leaves  black,  cupric  oxide. 

171.  Mercuric  Nitrate,  Hg(N03)2  +  8H20,  separates  in  large, 
colorless  crystals  when  we  cool  in  ice  and  salt  the  solution  obtained 
by  boiling  mercury  in  a  large  quantity  of  nitric  acid.     Its  solution 
is  an  energetic  caustic,  and  is  used  in  surgery.     When  dry  mer- 
curic nitrate  is  heated,  it  decomposes  just  as  the  nitrates  of  lead 
and  copper,  leaving  red  mercuric  oxide. 

Hg(N03)2    =     HgO     +     2N02     +     0 

172.  Lead  Nitrate,  Pb(N03)2. — This  compound,  which  is  one 
of  our  most  soluble  lead  salts,  is  made  by  boiling  lead  oxide  (lith- 
arge) in  nitric  acid,  and  evaporating  the  solution  until  crystals 
separate. 


PHOSPHORUS. 


119 


PbO     +     2HN03     =     Pb(N03)2     +     H20 

It  forms  colorless,  anhydrous  crystals,  very  soluble  in  boiling  water, 
an  1  in  seven  times  their  weight  of  cold  water. 


LESSON    XXTI. 

PHOSPHORUS.— HYDROGEN   PHOSPHIDE. 

173.  Phosphorus,  P=31. — The  element  phosphorus  is  extracted 
fr»  m  bones,  in  which  it  exists  in  a  compound  known  as  calcium 


FIG.  61. 

phosphate.  The  bones  are  first  burned,  to  remove  all  of  the  ani- 
mal matters,  and,  by  a  process  which  we  will  understand  better 
when  we  study  the  acids  of  phosphorus,  the  calcium  phosphate 
which  remains  is  converted  into  calcium  metaphosphate.  This 
last  body  is  mixed  with  charcoal  and  strongly  heated  in  clay  retorts, 
and  the  phosphorus  vapor  is  condensed  in  vessels  containing  cold 
water  (Fig.  61).  In  the  reaction  which  takes  place,  only  half  of 
the  phosphorus  is  separated  from  the  boiie-ash,  and  there  is  left  in 


120  LESSONS    IN   CHEMISTRY. 

the  retorts  a  compound  called  calcium  pyrophosphate,  while  the 
gas  carbon  monoxide  is  disengaged.  The  reaction  is  somewhat 
complicated. 

2Ca(P03)2  +     50     =  Ca2P207         •    +  5CO  +  P2 

Calcium  metaphosphate.     Carbon.      Calcium  pyrophosphate.     Carbon  monoxide. 

Small  particles  of  charcoal  are  carried  over  with  the  phos- 
phorus, which  is  purified  by  enclosing  it  in  chamois-skin  bags  and 
melting  it  under  warm  water.  The  melted  phosphorus  is  then 
squeezed  through  the  leather,  and  so  purified  is  drawn  up  into 
glass  tubes,  where  it  is  allowed  to  harden  in  the  form  of  sticks.  It 
is  always  kept  under  water,  and  is  transported  in  sealed  tin  cans. 

174.  PROPERTIES. — Phosphorus  is  an  almost  colorless,  wax- 
like  solid.     It  is  flexible,  and  soft  enough  to  be  readily  scratched 
by  the  finger-nail.     When  it  has  been  exposed  to  light  for  a  long 
time,  its  surface  becomes  white  and  opaque ;  it  is  covered  with 
little  crystals  of  phosphorus ;  these  become  loosened,  and  if  we 
shake  the  bottle  in  the  dark  the  whole  of  the  liquid  is  luminous. 
Phosphorus  has  a  peculiar,  somewhat  garlicky  odor.     Its  density 
is  1.83.     It  melts  at  44°,  and   boils  at  290°.     Its  density  com- 
pared to  hydrogen  is  62*  the  densities  of  its  gaseous  compounds, 
and  the  composition  of  all  its  compounds,  show  that  its  atomic 
weight  is  31  ;  therefore  the  molecule  of  phosphorus  vapor  must 
contain  four  atoms,  if  the  molecule  of  hydrogen   contains  two. 
That  is,  two  volumes  of  hydrogen  weighing  2  represent  two  atoms, 
but  two  volumes  of  phosphorus  vapor  weighing  124  contain  four 
atoms.     A  number  of  other  elements  also  have  molecules  contain- 
ing four  atoms.     Phosphorus  is  insoluble  in  water,  but  dissolves 
slightly  in  most  oils :  it  dissolves  freely  in  carbon  disulphide,  and 
separates  in  small  crystals  when  the  solution  is  evaporated  very 
slowly.    Phosphorus  is  luminous  in  the  dark,  and  this  phenomenon 
is  probably  caused  by  a  slow  oxidation. 

175.  Phosphorus  has  an  energetic  affinity  for  oxygen.     If  we 
expose  to  the  air  a  small  piece  of  dry  phosphorus  on  a  plate,  after 
a  time  the  heat  developed  by  the  slow  combustion  is  sufficient  to 
ignite  the  phosphorus,  which  takes  fire  at  a  temperature  of  50°. 
If  we  pour  on  a  piece  of  dry  paper  on  a  plate  a  few  cubic  centi- 


AMORPHOUS  PHOSPHORUS.  121 

nu  tres  of  a  solution  of  phosphorus  in  carbon  disulphide,  the  latter 
evaporates,  leaving  the  phosphorus  in  a  state  of  fine  division. 
Tlese  small  particles  are  surrounded  by  oxygen,  and  the  tem- 
pe'-ature  quickly  rises  till  they  burst  into  flame. 

Phosphorus  is  very  poisonous  :  even  when  poisoning  by  it  is  not 
rajiidly  followed  by  death,  dangerous  diseases  of  tne  liver,  heart, 
ki<  Ineys,  and  tongue  are  produced,  and  these  are  usually  fatal. 

176.  Amorphous  Phosphorus. — The  properties  which  have 
just  been  described  are  those  of  the.common  form  of  phosphorus, 
bu  t  there  is  another  form  which  may  be  obtained  by  heating  ordi- 
n  a  j  phosphorus  for  a  long   time    to   240°.      It  then   becomes 
bi'"Wnish  red,  opaque,  and  amorphous.     It  is  not  luminous  in  the 
da  k,  does  not  melt  at  44°  nor  take  fire  at  50°,  is  insoluble  in 
ca'bon  disulphide,  and  is  not  poisonous.     We  may  easily  make  a 
lit  le  of  this  red  phosphorus.     We  put  a  piece  of  dry  phosphorus 
in  a  test-tube,  and  drop  on  it  a  very  small  flake  of  iodine :  the 
iot  ine  combines  violently  with  part  of  the  phosphorus,  producing 
litLi  it  and  heat ;  but  the  remainder  of  the  phosphorus  has  become 
a  ]  ard  black  mass,  to  extract  which  we  must  probably  break  the 
tul  >e.     This  black  substance  is  amorphous  phosphorus,  and  when 
po  vdered  is  brown. 

While  amorphous  phosphorus  does  not  take  fire  as  readily  as 
ordinary  phosphorus,  its  chemical  properties  are  unchanged.  We 
mi  v  a  small  quantity  of  moist  amorphous  phosphorus  with  pow- 
deied  potassium  chlorate,  and  distribute  the  mixture  on  several 
pieces  of  paper  which  we  set  aside  to  dry.  When  quite  dry,  the 
least  pressure  on  the  spot  containing  the  mixture  will  cause  the 
oxidation  of  the  phosphorus  and  decomposition  of  the  potassium 
chlorate  with  a  loud  explosion. 

When  amorphous  phosphorus  is  heated  to  260°,  it  again 
changes  into  ordinary  phosphorus. 

177.  Large  quantities  of  phosphorus  are    employed   for   the 
manufacture  of  matches.     The  flame  of  phosphorus  alone  would 
not  ignite  the  stick,  because  this  would  become  coated  with  the 
phosphoric  oxide  formed,  and  the  latter  is  a  bad  conductor  of 
heat.     Common  matches  are  therefore  first  tipped  with  a  paste  of 

F  11 


122 


LESSONS    IN    CHEMISTRY. 


sulphur,  which  may  take  fire  from  the  phosphorus,  and  the  ends 
of  the  sticks  are  then  dipped  in  a  paste  of  ordinary  phosphorus 
with  strong  glue  and  some  coloring  matter.  The  brown-headed 
or  parlor  matches  are  tipped  with  a  paste  made  of  amorphous 
phosphorus  and  potassium  chlorate,  and  sometimes  antimony  sul- 
phide. The  safety  matches,  which  light  only  on  the  box,  contain 
the  potassium  chlorate  and  antimony  sulphide,  and  these  are 
ignited  by  friction  with  amorphous  phosphorus  glued  to  the  side 
of  the  box. 

Burns  by  phosphorus  are  quite  painful  and  difficult  to  heal. 
They  are  really  poisoned  wounds,  for  part  of  the  metaphosphoric 
acid  (§  187),  formed  by  the  action  of  the  phosphoric  oxide  on 
the  skin,  is  absorbed,  and  the  gravity  of  the  burn  is  much  greater 
than  that  of  an  ordinary  burn  of  the  same  size.  Phosphorus 
should  always  be  cut  under  water,  and  removed  from  the  water 
and  dried  between  folds  of  filter-paper  only  at  the  instant  before 
using. 

178.  Hydrogen  Phosphide,  PH3. — In  a  small  glass  retort 
which  we  have  completely  filled  with  a  rather  strong  solution  of 

•sodium  hydrate,  we  put  some 
small  pieces  of  phosphorus, 
and  after  arranging  the  beak 
of  the  retort  under  the  sur- 
face of  water  contained  in  a 
small  vessel,  we  apply  a  gentle 
heat  (Fig.  62).  When  the 
liquid  begins  to  boil,  bubbles 
of  gas  rise  through  the  water, 
and  as  each  bubble  comes 
into  the  air  it  takes  fire  and  produces  a  ring  of  white  smoke. 
When  the  air  is  perfectly  still,  we  notice  the  curious  motions  of  the 
rings.  The  gas  which  is  being  formed  is  hydrogen  phosphide, 
having  the  composition  PH3,  and  as  it  burns  the  hydrogen  is 
converted  into  water,  and  the  phosphorus  into  phosphoric  oxide 
which  forms  the  wreaths  of  smoke.  Hydrogen  phosphide  is  not, 
however,  the  only  product  of  the  reaction.  Part  of  the  phos- 


FIG.  62. 


OXIDES    AND    ACIDS    OF    PHOSPHORUS.  123 

pliorus  has  been  oxidized  at  the  expense  of  some  decomposed 
w  iter,  and  the  sodium  has  entered  into  the  new  molecule.  As  we 
know  by  analysis  that  only  sodium  hypophosphite,  having  the 
composition  NaH2P02,  and  hydrogen  phosphide  are  formed,  we 
may  write  the  rather  difficult  reaction, 

SNaOH         +      P*     +     3H20  3NaH2P02  +  PH3 

>  ..Hum  hydrate.  Sodium  hypophosphite. 

We  must  notice  that  the  molecule  of  hydrogen  phosphide  has 
a  composition  like  that  of  ammonia,  NH3.  Indeed,  it  will  under 
p  'oper  conditions  combine  directly  with  acids,  like  ammonia,  and 
its  compounds,  which  then  contain  the  group  PH4,  are  called 
p  losphonium  salts. 

If  we  heat  red  hot  in  an  earthen  crucible  some  fragments  of  quick-lime,  and, 
h  ving  a  cover  for  one  crucible,  throw  in  some  pieces  of  phosphorus,  covering 
tl  e  crucible  after  introducing  each  piece,  a  calcium  phosphide  is  formed  in 
tl  «  crucible.  When  the  crucible  and  contents  have  cooled,  we  may  throw  some 
(>•  the  pieces  of  the  calcium  phosphide  into  water;  bubbles  of  hydrogen  phos- 
ji  ilde  then  come  to  the  surface  and  take  fire  spontaneously,  forming  wreaths  of 
PI  loke  as  before.  Pure  hydrogen  phosphide  does  not  take  fire  on  coming  into 
tl  o  air,  unless  the  water  through  which  it  passes  is  boiling.  That  which  we 
h  ve  just  prepared  contains  a  trace  of  another  compound  of  phosphorus  and 
h  drogen  which  is  spontaneously  inflammable. 

179.  Phosphorus  Chlorides. — There  are  two  chlorides  of  phosphorus. 
Phosphorus  trichloride,  PCI3,  is  a  volatile,  colorless  liquid.  It  is  made  by  pass- 
ing chlorine  over  phosphorus  and  condensing  the  vapor  which  distils.  Phos- 
phorus pentachloride,  PCI5,  is  a  pale  yellow,  crystalline  solid.  It  is  obtained 
b\  passing  chlorine  into  the  trichloride  until  the  whole  becomes  solid.  Both 
ot  these  bodies  are  decomposed  by  water,  as  we  shall  presently  see. 


LESSON    XXIII. 
OXIDES   AND   ACIDS   OF  PHOSPHORUS. 

180.  There  are  two  oxides  of  phosphorus,  a  trioxide,  P203,  and 
a  pentoxide,  P205.  The  trioxide  is  formed  when  phosphorus  is 
slowly  oxidized  in  dry  air.  The  pentoxide,  often  called  phosphoric 
oxide,  results  when  phosphorus  is  burned  in  a  full  supply  of  air 


124  LESSONS    IN    CHEMISTRY. 

or  oxygen.  We  place  a  piece  of  phosphorus  in  a  small  dish  on 
a  plate,  and,  after  igniting  it,  cover  the  dish  with  a  bell-jar.  In  a 
short  time  the  phosphoric  oxide  formed  settles  on  the  dish  and 
sides  of  the  jar  in  the  form  of  a  snowy-white  powder.  When  we 
sprinkle  some  drops  of  water  on  this  powder,  a  hissing  noise  is 
heard ;  the  water  and  phosphoric  oxide  combine,  producing  much 
heat  and  an  acid  of  phosphorus.  The  composition  of  the  acid 
which  is  formed  depends  on  the  quantity  of  water  present, 
for  one  molecule  of  this  same  phosphoric  oxide  is  able  to  react 
with  one,  two,  or  three  molecules  of  water,  forming  three  different 

acids. 

P2Q5  +  H20  -  2HP03,  Metaphosphoric  acid. 

P205  +  2H20  =  H4P207,  Pyrophosphoric  acid. 

P2Q5  +  3H20  =  2H3P04,  Orthophosphoric  acid. 

We  shall  presently  study  these  acids.  Besides  these  there  are 
two  others.  Of  one  we  have  seen  the  formation  of  a  salt,  sodium 
hypophosphite ;  the  corresponding  acid  is  of  course  hypophos- 
phorous  acid,  H3P02.  The  other  is  formed  by  the  reaction  of 
phosphorus  trioxide  on  water,  and  one  molecule  of  the  trioxide 
reacts  with  three  molecules  of  water,  forming  two  molecules  of 
phosphorous  acid. 

We  then  have  a  series  of  acids. 

H3P02,  Hypophosphorous  acid. 

H3P03,  Phosphorous  acid. 

H3P04,  Orthophosphoric  acid. 

H*P207,  Pyrophosphoric  acid. 

HPO3,  Metaphosphoric  acid. 

181.  Hypophosphorous  Acid  may  be  made  by  boiling  phos- 
phorus with  barium  hydrate,  Ba(OH)2,  and  by  the  cautious  addi- 
tion of  sulphuric  acid  exactly  precipitating  the  barium  from  the 
barium  hypophosphite  formed.  After  filtering,  the  liquid  is  con- 
centrated until  a  thick  syrup  is  obtained.  This  is  hypophosphorous 
acid.  Although  a  molecule  of  this  acid  contains  three  atoms  of 
hydrogen,  only  one  of  those  atoms  is  replaceable  by  metal.  It  is 
a  monobasic  acid,  and  its  salts  with  a  monatomic  metal  like  sodium 
will  contain  one  atom  of  metal  and  the  group  H2P02.  The  hypo- 
phosphites  of  diatomic  metals  must  contain  two  of  these  groups 


ORTHOPHOSPHORIC    ACID.  125 

in  order  that  two  atoms  of  hydrogen  may  be  replaced :  barium 
hypophosphite  will,  then,  be  Ba(H2P02)2. 

182.  Phosphorous  Acid  is  most  quickly  prepared  by  the  re- 
aeiion  of  phosphorus  trichloride  with  water,  one  molecule  of  the 
trichloride  requiring  three  molecules  of  water. 

PCI3     +     3H20     =     H3P03     +     3HC1 

It  is  a  dibasic  acid:  it  contains  two  atoms  of  replaceable  hydro- 
gt  i;  we  may  have  a  sodium  phosphite,  Na2HP03,  and  a  sodium 
ac  d  phosphite,  NaH2P03.  Barium  phosphite  would  be  BaHPO3. 
Both  hypophosphorous  and  phosphorous  acids  have  reducing 
pi  >perties ;  that  is,  they  will  take  away  oxygen  from  oxidized 
b<  lies,  so  becoming  converted  into  phosphoric  acid.  Into  a  test- 
tu  je  containing  a  solution  of  silver  nitrate,  we  pour  some  solution 
of  sodium  hypophosphite  :  in  a  short  time  the  interior  of  the  tube 
is  coated  with  metallic  silver  by  the  reducing  action  of  the  hypo- 
pi  osphite. 

183.  Orthophosphoric  Acid. — We  have  seen  how  this  acid, 
wiiich  is  commonly  called  phosphoric  acid,  may  result  from  the 
ac  ion  of  water  on  phosphoric  oxide.     It  is  also  formed  by  the 
reaction  of  phosphorus  pentachloride  with  water. 

PCI5     +     4H20     =       H3P04     +     5HC1 

It  is  usually  made  by  boiling  amorphous  phosphorus  with  nitric 
ac  d,  which  is  reduced,  red  vapors  being  given  off.  The  liquid  is 
th'.-n  evaporated  to  a  small  bulk,  and  put  in  a  bell-jar  over  a  dish 
co'itaining  sulphuric  acid,  which  gradually  absorbs  the  remain- 
ing moisture.  In  this  manner  hard,  transparent,  and  deliquescent 
crystals  of  orthophosphoric  acid  are  obtained. 

Orthophosphoric  acid  is  tribasic :  its  molecule  contains  three 
atoms  of  replaceable  hydrogen.  Consequently  it  may  with  the 
same  metal  form  three  different  salts,  accordingly  as  one,  two,  or 
three  atoms  of  hydrogen  are  replaced  by  a  corresponding  quantity 
of  the  metal.  The  names  of  these  salts  should  indicate  the  number 
of  hydrogen  atoms  which  have  been  replaced,  or  the  number  of 
metallic  atoms  which  have  replaced  the  hydrogen  :  thus,  since  one 
atom  of  sodium  always  replaces  one  of  hydrogen,  monosodi.um 
phosphate  is  NaH2P04,  disodium  phosphate  is  Na2HP04,  and  tri- 
ll* 


126  LESSONS    IN    CHEMISTRY. 

sodium  phosphate  is  Na3P04.  We  have  already  learned  by  several 
reactions  (§§  118,  136)  that  one  atom  of  calcium  is  capable  of  re- 
placing two  atoms  of  hydrogen  ;  and  if  we  perfectly  neutralize 
orthophosphoric  acid  with  lime  (calcium  oxide),  we  must  have 
two  molecules  of  the  acid  and  three  of  lime. 

2R3PO*  +  3CaO  =  Ca3(PO*)2  +  3  IPO 
The  tricalcium  phosphate  so  formed  is  the  compound  existing 
in  bone-ash,  from  which  phosphorus  is  obtained.  It  is  insoluble 
in  water ;  when  it  is  treated  with  sulphuric  acid,  two  atoms  of 
calcium  are  taken  from  its  molecule,  forming  calcium  sulphate, 
while  calcium  acid  phosphate  passes  into  the  solution. 

Ca3(P04)2       +      2H2SO*  CaH*PO*  +         2CaSO* 

Tricalcium  phosphate.  Calcium  acid  phosphate.      Calcium  sulphate. 

The  calcium  sulphate,  being  insoluble,  is  separated  by  filtration, 
and  the  calcium  acid  phosphate  is  converted  into  calcium  meta- 
phosphate  by  the  action  of  heat,  which  decomposes  it  with  the 
formation  of  water. 

CaH*PO*  Ca(P03)2  +     2R2Q 

Calcium  acid  phosphate.        Calcium  metaphosphate. 

184.  To  a  solution  of  disodium  phosphate — either  of  the  other 
orthophosphates  would  answer — we  add  a  little  ammonia-water, 
and  then  some  magnesium  sulphate  solution.     A  white  precipitate 
forms ;  this  contains  both  ammonium  and  magnesium  ;  two  atoms 
of  hydrogen  in  phosphoric  acid  are  here  replaced  by  one  atom  of 
magnesium,  and  the  other  by  the  ammonium  group,  NHV 

Na2HPO*    +     MgSO4     +  Nfl3  =    Na2S04      +      Mg(NR4)PO* 
Disodium  Magnesium  Sodium  Ammonio- 

phosphate.  sulphate.  sulphate.       magnesium  phosphate. 

In  another  test-tube  we  mix  some  solutions  of  disodium  phos- 
phate and  silver  nitrate.  A  yellow  precipitate  of  trisilver  phos-t 
phate  forms. 

Na2HPO*     +     3AgN03     =     AgSPO*     +     2NaN03     -f     HNO3 

These  reactions  enable  us  to  identify  orthophosphoric  acid  and 
the  orthophosphates. 

185.  ORTHOPHOSPHATES. — Disodium  phosphate  exists  in  the 
blood,  and  the  phosphorus  which  is  eliminated  from  our  bodies  is 


PYROPHOSPIIORIC    ACID.  127 

piincipally  in  monosodium  phosphate,  which  passes  out  in  the 
urine.  The  phosphates  containing  only  one  atom  of  metal  redden 
blue  litmus,  and  are  generally  called  acid  phosphates.  Those 
c<  ntaining  two  atoms  of  metal  do  not  affect  litmus,  and  are  gen- 
ei ally  called  neutral  or  common  phosphates;  while  those  having 
tl  ree  atoms  of  metal  turn  red  litmus  to  blue. 

Large  mineral  deposits  of  tricalcium  phosphate  exist  in  many 
li  calities,  and  it  is  probable  that  they  have  been  formed  from  ac- 
cumulations of  bones  during  prehistoric  ages.  The  mineral  apa- 
ti  'e,  generally  green  in  color,  is  principally  tricalcium  phosphate. 

186.  Pyrophosphoric  Acid. — When  orthophosphoric  acid  is 
1(  ng  heated  to  a  temperature  of  about  213°,  it  undergoes  partial 
d  ;composition  :  two  molecules  lose  one  molecule  of  water,  and  then 
C'  mbine  together,  forming  a  molecule  of  pyrophosphoric  acid. 

2H3PO*    =      H20    +    H4P207 

We  can  understand  this  better  if  we  consider  the  structure  of  the  molecule 
o:  phosphoric  acid:  it  must  contain  three  hydroxyl  groups,  and  the  other 
ai  >rn  of  oxygen  must  be  combined  directly  with  the  phosphorus  atom.  By  the 
K  inoval  of  the  elements  of  one  molecule  of  water,  two  groups,  each  containing 
01  e  phosphorus  atom,  one  oxygen  atom,  and  two  hydroxyl  groups,  will  be 
ci  nented,  we  may  say,  by  an  atom  of  oxygen. 

OH  OH  OH    OH 

HO-P^O  +  HO-P^O  O^P-0-P^O         •+  HOH 

OH  OH  OH    OH 

Two  molecules  orthophosphoric  acid.  Pyrophosphoric  acid. 

W3  see  then  that  in  certain  compounds,  such  as  hydrogen  phosphide  and 
plosphorus  trichloride,  phosphorus  is  triatomic,  but  that  in  other  cases,  and 
th -se  are  the  most  numerous,  it  is  pentatomic,  or  equivalent  to  five  atoms  of 
h  ydrogen. 

We  mix  some  solutions  of  sodium  pyrophosphate  and  silver 
nitrate ;  instantly  a  white  precipitate  of  insoluble  silver  pyrophos- 
phate  is  formed. 

Na4P207     +     4AgN03     =     Ag*P207     +     4NaN03 

187.  Metaphosphoric    Acid, — When   either  orthophosphoric 
or  pyrophosphoric  acid  is  heated  to  redness,  water  is  formed,  and 
there  remains  a  hard,  glass-like  mass  of  metaphosphoric  acid. 

H3PO*    .      II PO3    +    H20 


128  LESSONS    IN.   CHEMISTRY. 

If  an  acid  phosphate  is  heated  in  the  same  manner,  it  undergoes 
a  similar  decomposition,  and  a  metaphosphate  remains  (§  183). 

Metaphosphoric  acid  quickly  coagulates  or  renders  insoluble  the 
albumen  of  white  of  egg,  a  property  which  distinguishes  it  from 
both  ortho-  and  pyrophosphoric  acids. 

Metaphosphoric  and  pyrophosphoric  acids  and  their  salts  are 
poisonous,  as  are  also  hypophosphorous  and  phosphorous  acids,  but 
orthophosphoric  acid  and  the  orthophosphates  are  not  poisonous 
unless  in  such  concentrated  form  as  to  be  corrosive. 

188.  When  either  metaphosphoric  or  pyrophosphoric  acid,  or 
any  of  their  salts,  is  boiled  with  nitric  acid,  orthophosphoric  acid  or 
one  of  its  salts  is  formed.  We  have  already  seen  that  phosphorus 
itself  is  oxidized  to  orthophosphoric  acid  by  nitric  acid.  If 
to  this  solution  in  nitric  acid  we  add  a  solution  of  ammonium 
molybdate  also  in  nitric  acid,  at  once  or  after  a  time  a  bright- 
yellow  precipitate  of  a  body  called  ammonium  phosphomolybdate 
separates.  In  this  manner  we  can  detect  the  presence  of  phos- 
phorus or  any  of  its  compounds. 


LESSON    XXIV. 
ARSENIC.     As  =  75. 

189.  Arsenic  is   found  associated  with   many  metals,  copper, 
silver,  bismuth,  nickel,  but  it  is  obtained  principally  from  one  of 
its  minerals,  which  contains  also  iron  and  sulphur.     This  mineral 
is  called  mispickel,  and  its  composition  may  be  represented  by  the 
formula  FeSAs.    When  it  is  strongly  heated,  the  arsenic  is  driven 
out,  and  iron  sulphide,  FeS,  remains.     The  operation  is  conducted 
in  clay  retorts,  and  the  arsenic  condenses  in  sheet-iron  receivers. 
This  impure  arsenic  is  generally  sold  under  the  name  cobalt ;  it  is 
purified  by  being  redistilled  out  of  contact  with  air. 

190.  In  a  small  test-tube  we  heat  some  commercial  arsenic,  and 
soon  a  bright  steel-gray  ring  forms  in  the  cooler  part  of  the  tube ; 
after  a  time  the  interior  of  the  ring  becomes  lined  with  small  but 


ARSENIC.  129 

brilliant  metallic  crystals.  This  is  the  appearance  of  arsenic,  but 
its  surface  oxidizes  after  some  exposure  to  the  air,  and  becomes 
tarnished.  The  density  of  arsenic  is  5.7.  It  does  not  melt  when 
heated  ;  it  sublimes;  but  it  may  be  melted  to  a  transparent  liquid 
by  heating  it  under  pressure.  It  is  insoluble  in  water,  but  is 
slovly  oxidized  by  the  air  dissolved  in  the  water,  and  the  oxide 
dis  olves,  rendering  the  water  poisonous.  When  arsenic  is  heated 
in  ontact  with  air,  it  volatilizes,  and  its  vapor  is  oxidized  to  white 
ars  'nious  oxide.  Arsenic  takes  fire  spontaneously  in  chlorine, 
bir  iiing  into  arsenic  chloride,  AsCl3,  which  is  a  volatile,  very  poi- 
soi. ous  liquid. 

A  SUM.;!  quantity  of  arsenic  is  added  to  the  lead  for  making 
she  t  ;  it  hardens  the  shot,  and  the  interior  of  the  gun-barrel  does 
not  become  coated  with  lead  by  friction  with  that  soft  metal. 

.91.  Arsenious  Oxide,  As203. — We  heat  a  very  small  frag- 
mc  it  of  arsenic  in  a  test-tube,  and  presently  a  white  ring  con- 
dci  ses  on  the  sides  of  the  tube.  The  arsenic  has  been  oxidized, 
am  the  volatile  oxide  has  condensed  in  the  tube  :  if  we  examine 
the  ring  by  the  aid  of  a  good  microscope,  we  find  that  it  is  com- 
po.-3d  of  small,  eight-sided  crystals.  These  are  arsenious  oxide. 
Ar;enious  oxide  is  manufactured  in  this  manner,  by  heating 
ars  ?nic  in  contact  with  the  air,  and  the  vapor  is  condensed  either 
in  cool  chimneys  or  in  large  rooms.  As  it  is  a  very  poisonous 
sulstance,  the  operation  is  conducted  with  all  possible  precaution 
that  the  workmen  may  not  inhale  the  vapors  and  dust. 

When  it  is  freshly  sublimed  in  large  masses,  arsenious  oxide  is 
a  glassy,  transparent,  and  amorphous  solid,  but  it  soon  becomes 
opaque,  and  this  is  due  to  the  formation  of  little  crystals.  It  is 
not  very  soluble  in  water,  and  the  amorphous  form  is  more  sol- 
uble than  the  crystalline  or  opaque  variety.  Amorphous  arsenious 
oxide  dissolves  in  twenty-five  times  its  weight  of  cold  water,  but 
the  crystalline  form  requires  eighty  times  its  weight.  The  solution 
contains  arsenious  acid,  but  when  we  evaporate  the  liquid  and  try 
to  separate  this  acid,  it  is  again  decomposed  into  arsenious  oxide 

and  water. 

As203  +  3H20  2H3AsO» 

Arsenious  oxide.  Water.  Arsenious  acid. 


130  LESSONS    IN    CHEMISTRY. 

Because  arsenious  oxide  is  frequently  the  cause  of  intentional 
or  accidental  poisoning,  it  is  important  that  we  shall  be  able  to 
recognize  it;  but  we  will  better  understand  its  tests  when  we  have 
learned  something  of  the  other  compounds  of  arsenic. 

192.  Arsenic  Oxide  and  Acids. — When  arsenic  or  arsenious 
acid  is  boiled  with  nitric  acid,  it  is  oxidized  just  as  phosphorus 
was  oxidized,  and  the  ortho-arsenic  acid  formed  corresponds  ex- 
actly to  orthophosphoric  acid.     It  contains  H3As04.     When  it  is 
heated  to  150°.  it  is  decomposed  like  orthophosphoric  acid,  and 
pyroarsenic  acid,  H4As207,  is  formed.     This  also  is  decomposed 
at  200°,  yielding  metarsenic  acid,  HA^O3,  which  when  heated  to 
redness  loses  the  elements  of  water,  and  leaves  arsenic  oxide,  As205. 

?H3AsO*     =     H4As207     +     H2Q         H4As207     =     2HAs03     +     IPO 
2HAs03     =     As205     +     H20 

193.  We  boil  a  few  grains  of  arsenious  oxide  with  a  few  drops 
of  nitric  acid  in  a  test-tube,  and   when   the  last  particle  of  the 
solid  disappears,  we  carefully  neutralize  the  liquid  with  ammonia. 
Now  when  we  add  some  silver  nitrate  solution,  a  brick-red  pre- 
cipitate of  silver  arsenate  is  formed. 

(NH4)3As04  +         3AgN03        =         Ag3As,04       +         3NH4N03 

Ammonium  arsenate.  Silver  nitrate.  Silver  arsenate.      Ammonium  nitrate. 

194.  Arsenic  Sulphides. — In  a  test-tube  of  hard  glass  we 
melt  together  some  powdered  arsenic  mixed  with  a  little  more 
than  half  its  weight  of  sulphur.     After  cooling,  the  liquid  solidi- 
fies to  a  red  mass  of  arsenic  disidphide,  As2S2.     This  substance 
is  commonly  called  realgar.     It  is  found  as  a  mineral  in  trans- 
parent red  prisms.     It  is  insoluble  in  water.     When  heated  in 
the  air,  both  its  arsenic  and  sulphur  burn,  yielding  arsenious  oxide 
and  sulphur  dioxide. 

In  another  test-tube  we  melt  a  mixture  of  powdered  arsenic 
with  about  two-thirds  its  weight  of  sulphur.  When  this  tube 
cools,  we  find  in  it  yellow  arsenic  trisulphide,  As2S3,  generally 
called  orpiment.  This  sulphide  also  is  found  as  a  mineral.  It  is 
insoluble  in  water,  but  if  boiled  for  a  long  time  with  that  liquid 
it  is  decomposed,  yielding  hydrogen  sulphide  and  arsenious  acid. 
As2S3  +  6H20  =  2H3As03  + 


TESTS    FOR    ARSENIC. 


131 


Conversely,  by  passing  hydrogen  sulphide  through  a  solution 
of  arsenious  oxide  to  which  a  drop  of  hydrochloric  acid  has  been 
auded,  yellow  arsenious  sulphide  is  precipitated. 

195.  Tests  for  Arsenic. — Arsenious  oxide  and  some  of  its 
c<  mpounds  are  the  usual  forms  in  which  we  must  identify  arsenic. 
Ii    a  porcelain  evaporating  dish  we  heat  some  pure  water,  and 
\v  ien  it  boils  we  add  a  few  drops  of  hydrochloric  acid,  and  then 
p  it  in  a  thin  strip  of  bright  copper.     The  metal  does  not  tarnish  ; 
but  when  we  add  to  the  boiling  liquid  a  little  of  any  solution  cen- 
ts; ining  arsenic,  the  copper  soon  becomes  coated  with  a  steel-gray 
01  even  black  deposit,  which  is  a  compound  of  copper  and  arsenic. 
T'lis  is  called  Reinsch's  test.     We  take  this  slip  of  copper  from 
tl  e  liquid,  wash  it 

ii  pure  water,  and 
c;  refully  dry  it  be- 
t\  een  folds  of  warm 
fi  ter-paper.  Then 
\v  3  cut  it  into  sev- 
ei  ?il  very  narrow 
si  ps,  and  put  one 
01  two  of  these  in  a 
little  tube  drawn  out 
ai  d  sealed  at  one 
ei  d.  We  cover  this 
pbce  of  copper  with  some  warm  charcoal  powder,  and  then  heat 
the  end  of  the  tube.  The  heat  drives  the  arsenic  away  from  the 
copper,  and  the  charcoal  prevents  the  vapor  from  becoming  oxi- 
dized, so  that  a  gray  or  black  mirror  of  arsenic  condenses  in  the 
nearest  cool  part  of  the  tube  (Fig.  63). 

196.  In  another  similar  tube  we  put  another  piece  of  our  coated 
copper  foil,  and  heat  it  alone.     In  this  case  the  arsenic  vapor  be- 
comes oxidized  by  the  air  in  the  tube,  and  white  arsenious  oxide 
is  deposited  in  minute  octahedral  crystals  that  we  may  recognize 
when  we  examine  the  tube  under  the  microscope  (Fig.  64).    Were 
wo  to  break  off  the  portion  of  the  tube  containing  this  deposit, 
and  boil  it  with   a  very  little  water  in  another  tube,  we  would 


FIG.  63. 


132 


LESSONS    IN    CHEMISTRY. 


obtain  a  solution  of  arsenious  acid,  with  which  we  could  make  the 
next  tests ;  these,  however,  we  will  make  with  larger  quantities  of 
the  substance. 

197.  To  a  solution  of  arsenious  acid  in  a  test-tube,  we  add  a 
drop  of  ammonia,  and  then  some  silver  nitrate  solution.    A  canary- 
yellow  precipitate  of  insoluble  silver  arsenite  is  formed. 

(NH^HAsO3        +     2AgN03     =     2NH*N03     +       Ag2HAs03 
Ammonium  arseuite.  Silver  arsenite. 

198.  To  a  similar  solution,  treated  with  a  little  ammonia,  we 

add  cupric  sulphate  dissolved  in  water. 
An  apple-green  precipitate  of  cupric 
arsenite,  CuHAsO;!,  is  thrown  down. 

199.  In    another   tube  we    acidulate 
some  arsenious  acid  with  a  drop  of  hy- 
drochloric acid,  and  then  pass  hydrogen 
sulphide  through  the  liquid.     A  bright 
yellow  precipitate  of  arsenic  trisulphide 
is  formed. 

200.  When  arsenious  acid  is  poured 
into  a  bottle  in  which  hydrogen  is  being  generated,  the  nascent 
hydrogen,  that  is,  the  free  atoms  of  hydrogen  which  have  not 
exhausted  part  of  their  energy  by  combining  to  form  molecules, 
will  reduce  or  take  away  oxygen  from  the  arsenious  acid,  and 
combine  with  the  arsenic,  forming  an  exceedingly  poisonous  gas, 
of  which  we  must  be  careful  not  to  inhale  the  least  quantity.     It 
is  called  hydrogen  arsenide.     Its  molecule  contains  Asli3. 

H3As03     +     6H     =     3H20     +     AsH3 

We  have  prepared  a  hydrogen-bottle  with  a  long  jet  (Fig.  65), 
and,  while  the  hydrogen  is  burning  with  its  pale  flame  at  this  jet, 
we  pour  through  the  funnel-tube  a  few  drops  of  a  solution  of 
arsenious  oxide.  In  a  few  moments  the  flame  becomes  bluish  and 
elongated.  Hydrogen  arsenide  is  burning,  and  the  arsenic  oxidizes 
to  arsenious  oxide,  producing  a  white  smoke.  In  this  flame,  and 
close  to  the  jet,  we  hold  a  plate  or  piece  of  cold  porcelain,  which 
will  prevent  the  arsenic  from  getting  enough  oxygen  to  become 
oxidized.  We  see  a  dark  spot  of  arsenic  forming,  and  we  make 


FIG.  64. 


TESTS    FOR    ARSENIC. 


133 


si  veral  of  these  spots  on  different  portions  of  the  plate.    This  is 

ci.lled  Marsh's  test.     If  with  a  lamp  we  heat  the  tube  of  the  long 

jet,  the  hydrogen  arsenide 

will    be    decomposed    by 

tl  e    heat,   and    the    dark 

ri'ig  of  arsenic  deposited 

ii    the  cooler  part  of  the 

ti  be    may  be    afterwards 

ti  sted  as  we  have  already 

st  udied. 

201.  We     connect     a 
li  tie  bent  tube  with  our 
j- t,  and  pass  the  gas  into 
si  me  silver  nitrate  solution 
ii   a  test-tube  ;  a  black  de- 
p-  sit  of  silver  separates, 

ai  d     arsenious     acid     is  FIG.  65. 

frrmed  in  the  solution. 

AsH3     +     6AgN03     +     3H20     =     H3As03     +     6HN03     +     Ag6 
"W  e  filter  the  liquid  from  the  silver,  and  add  a  drop  of  ammonia ; 
if  all  of  the  silver  nitrate   has   not  been   decomposed,  a  yellow 
piecipitate  of  silver  arsenite  is  formed.     We  may  be  obliged  to  add 
a  "ew  more  drops  of  silver  nitrate  (§  197). 

202.  Now  we  touch  one  of  the  spots  on  our  plate  with  a  drop 
of  strong  nitric  acid.     The  spot  disappears :  we  add  a  small  drop 
of  ammonia,  and  cautiously  warm  the  plate  until  it  is  dry.    Then 
we  touch  it  with  a  drop  of  silver  nitrate,  and  it  becomes  brick-red 
from  the  formation  of  silver  arsenate  (§  193). 

All  of  these  tests  enable  us  to  recognize  arsenic  with  certainty; 
they  are  applied  to  substances  which  are  extracted  from  the  body 
in  cases  of  supposed  poisoning. 

The  green  coloring  matters  known  as  Scheele's  green  and  Paris 
green  are  compounds  containing  arsenic  and  copper :  they  are 
exceedingly  poisonous. 


12 


134  LESSONS    IN    CHEMISTRY. 


LESSON    XXV. 

ANTIMONY.     Sb  (Stibium)  =  120. 

203.  Antimony  is  found  principally  in  combination  with  sulphur 
in  a  grayish-black  mineral,  antimony  sulphide,  Sb2S3.  This  sul- 
phide is  quite  fusible,  and  it  is  separated  from  the  earthy  matters 
with  which  it  is  mixed,  and  which  are  called  the  gangue,  simply 
by  heating  the  ore  ;  the  antimony  sulphide  melts  and  runs  out.  The 
easiest  method  of  obtaining  antimony  from  this  sulphide  is  to  mix 
the  powdered  sulphide  with  scrap  iron  and  heat  the  mixture  to 
redness  in  a  crucible.  Iron  sulphide  and  antimony  are  formed, 
and  the  latter,  being  the  heavier,  collects  at  the  bottom,  where  we 
find  it  as  a  bright  button-shaped  lump  when  we  break  the  cold 
crucible.  The  cheapest  method,  however,  is  to  roast  the  powdered 
sulphide ;  that  is,  heat  it  in  the  air ;  most  of  the  sulphur  is  then 
oxidized  to  sulphur  dioxide,  which  passes  off,  and  most  of  the  anti- 
mony is  converted  into  antimonous  oxide.  The  roasted  mass  is 
then  mixed  with  charcoal,  and  the  mixture  moistened  with  sodium 
hydrate,  after  which  it  is  heated  in  crucibles.  The  carbon  removes 
the  oxygen  from  the  antimony  oxide,  and  the  sodium  hydrate  re- 
moves the  sulphur  from  the  antimony  sulphide  still  present.  The 
sodium  sulphide  produced  forms  a  slag  which  floats  on  the  surface 
of  the  melted  antimony. 

PROPERTIES. — Antimony  is  a  very  brilliant,  white  substance, 
having  a  high  metallic  lustre.  It  is  very  brittle,  and  breaks 
in  shining  layers :  it  is  said  to  have  a  laminated  structure.  Its 
density  is  6.7.  It  melts  at  450°  ;  when  a  considerable  quantity 
of  it  is  melted  in  a  crucible  and  allowed  to  cool  quietly  until 
a  crust  forms  on  the  surface,  if  we  make  a  hole  in  this  crust  and 
pour  out  the  still  molten  interior,  the  crucible  will  be  found  to  be 
lined  with  small  shining  crystals. 

When  antimony  is  heated  in  the  air,  it  is  oxidized  to  antimo- 
nous oxide,  Sb203.  We  have  already  seen  that  antimony  burns 


ANTIMONY.  135 

spontaneously  when  thrown  into  chlorine.     It  combines  with  the 
chlorine,  forming  antimony  pentachloride,  SbCl5. 

Antimony  enters  into  the  composition  of  several  alloys.  Type- 
in  3tal  contains  twenty  per  cent,  of  antimony  and  eighty  per  cent, 
of  lead.  Lead  is  too  soft  for  type,  and  it  does  not  take  sharp  im- 
piessions  of  moulds:  the  antimony  renders  the  metal  hard,  and 
cruses  it  to  expand  on  solidifying,  so  filling  every  line  of  the 
ns  )uld.  Britannia  metal  also  contains  antimony. 

204.  Antimony  Chlorides. — By  distilling  antimony  trisulphide  with  hydro- 
ei  loric  acid,  and  collecting  apart  the  product  which  passes  after  the  condensed 
li   uid  begins  to  crystallize  in  the  neck  of  the  retort,  antimony  trichloride,  SbCl3, 
is  obtained  as  a  transparent,  colorless  solid,  melting  at  73°,  and  boiling  at  230°. 
It  is  soluble  in  dilute  hydrochloric  acid,  but  when  the  solution  is  diluted  with 
w  ter,  an  insoluble  oxychloride,  SbOCl,  is  thrown  down,  while  hydrochloric 
at  d  is  formed.     Antimony  pentachloride,  SbCl5,  is  a  volatile,  yellow  liquid, 
fu  med  by  the  action  of  an  excess  of  chlorine  on  antimony  or  the  trichloride. 

205.  Antimony  Oxides. — Antimonous  oxide,  Sb'203,  is  made  by  heating  anti- 
iii  my  to  redness  in  open  crucibles;  after  cooling,  the  latter  are  found  lined  with 
si  ming,  needle-like  crystals  of  the  oxide,  which  corresponds  in  composition  to 
ai  -enious  oxide.     When  antimony  is  boiled  with  strong  nitric  acid,  it  is  con- 
vc  rted  into  nietantimonic  acid,  HSbO3  ;  by  the  action  of  a  red  heat  this  is  de- 
co  nposed,  yielding  antimony  pentoxide,  Sb205.     There  is  also  a  pyrantimonic 
at  'd,  H4Sb207,  but  there  is  no  orthantiinonic  acid  of  the  composition  Il3SbO*. 

However,  this  acid,  which  would  have  threo  atoms  of  replaceable  hydrogen, 
is  represented  by  a  curious  compound  in  which  we  may  consider  that  those 
th  'ee  atoms  are  replaced  by  a  single  atom  of  antimony.  When  antimonous 
oxide  is  heated  for  a  long  time  in  the  air,  it  absorbs  oxygen,  and  the  resulting 
co  npound  has  the  composition  Sb'204,  which  we  may  write  Sb(Sb04). 

206.  Antimony  Trisulphide,  Sb2S3,  is  the  grayish-black  min- 
eral from  which  we  have  already  learned  that  antimony  is  obtained. 
It  is  a  heavy,  crystalline   substance,  having  a  marked  metallic 
appearance.     It  is  commonly  called  stibium.     This  same  sulphide 
may  be  obtained  in  another  form.     Through  a  solution  of  anti- 
nrjny   trichloride    we    pass  hydrogen   sulphide ;    an   amorphous, 
orange-colored  precipitate  is  formed,  and  this  is  antimony  trisul- 
phide. 

2SbCl3  +  3IPS  Sb2S3  +          6HC1 

Antimony  trichloride.  Antimony  trisulphide. 

207.  When  a  solution  containing  antimony  is  introduced  into 
i\  bottle  in  which  hydrogen  is  being  generated,  some  of  the  hydro- 


136  LESSONS    IN    CHEMISTRY. 

gen  combines  with  the  antimony,  producing  a  gas,  hydrogen  anti- 
monide.  Although  this  gas  has  not  been  obtained  in  a  pure  state, 
being  very  easily  decomposed,  enough  has  been  learned  about  it 
to  show  that  it  has  the  composition  SbH3.  It  causes  the  hydro- 
gen to  burn  with  a  bluish  flame,  somewhat  like  that  of  hydrogen 
arsenide,  and  it  also  produces  dark  spots  on  a  piece  of  porcelain 
held  in  the  flame,  as  well  as  rings  in  the  heated  tube  (§  200)  ;  but 
here  the  resemblance  with  arsenic  ceases.  When  the  spots  are 
oxidized  by  nitric  acid  and  then  treated  with  silver  nitrate,  no 
brick-red  color  is  produced.  When  the  gas  is  passed  through 
silver  nitrate  solution,  a  dark  compound  of  silver  and  antimony  is 
precipitated,  and,  as  the  clear  liquid  then  contains  only  nitric  acid, 
it  cannot  give  a  precipitate  when  neutralized  with  ammonia 
(§§  200-202). 

208.  When  we  compare  the  compounds  of  nitrogen,  phosphorus,  arsenic, 
and  antimony,  we  find  that  the  atoms  of  these  elements  are  almost  alike  as 
far  as  their  power  of  combining  is  concerned.     One  atom  of  each  will  combine 
with  three  atoms  of  hydrogen,  and  we  then  have  formed  the  four  gases, 

NR3  PH3  AsH3  SbH3 

Their  more  important  compounds  with  chlorine  show  the  same  similarity  : 
NCI3  PCI3  AsCl3  SbCl3 

But,  in  addition  to  these  chlorides,  phosphorus  and  antimony  form  penta- 
chlorides,  PCI5  and  SbCl5.  Each  of  the  four  elements  has  a  trioxide  and  a 
pentoxide,  and  from  each  of  the  pentoxides  is  derived  an  acid  containing  one 
atom  of  hydrogen,  one  atom  of  the  element,  and  three  atoms  of  oxygen : 

UNO3  HPO3  HAsO3  HSbO3 

In  addition,  phosphorus  and  arsenic  form  the  ortho-acids,  H3P04  and 
H3As04,  while  phosphorus,  arsenic,  and  antimony  form  the  pyro-acids,  H4P207, 
H4As20?,  and  H*Sb207. 

These  similarities  and  many  others  enable  us  to  group  together  the  four  ele- 
ments in  a  natural  class;  since  in  their  compounds  one  atom  of  either  of  the 
class  has  a  combining  power  equal  to  that  of  three  or  of  five  atoms  of  hydro- 
gen, we  may  call  the  class  the  group  of  triatomic  or  pentatomic  non-metals. 

209.  There  are  three  other  elements  which  would  be  placed  in  the  class  that 
we  have  just  considered,  but  they  occur  in  such  small  quantities,  although 
widely  distributed,  that  we  can  only  mention  their  names.     They  are  vana- 
dium, niobium,  and  tantalum.     They  are  found  in  the  minerals  vanadanite, 
columbite,  and  some  others. 


BORON.  137 

LESSON    XXV  I. 

BORON.    B  =  ii. 

210.  The  well-known  substance,  borax,  is  a  compound  of  the 
e  emeut  boron.     To  a  saturated  solution  of  borax  we  add  some 
f-  ilphuric  acid  :  soon  there  separates  a  deposit  composed  of  small 
v  hite  flakes.     If  we  filter  these  flakes  from  the  liquid,  and  dry 
t  lem,  we  have  pearly  white  scales  which  feel  greasy  like  soap 
vhen  we  take  them  between  the  fingers.     This  substance  is  boric 
n  -id  ;  it  contains  H3B03.      If  we  heat  it  red  hot  in  a  platinum 
c  'ucible,  it  decomposes  and  leaves  boric  oxide,  B203. 

2II3B03  =  3H20  +  B203 

When  this  boric  oxide  is  mixed  with  pieces  of  sodium,  some 
c  (ttimon  salt  being  added  to  make  the  mixture  melt  more  readily, 
;i  id  heated  to  bright  redness  in  a  covered  iron  crucible,  sodium 
lorate  and  boron  are  formed. 

3Na2         +         2B203  2Na3B03         +         B2 

Boric  oxide.  Sodium  borate. 

A  fter  the  crucible  has  cooled,  the  fused  mass  is  treated  with  dilute 
hydrochloric  acid,  which  dissolves  the  sodium  borate,  leaving  the 
boron  as  a  dark-brown  or  olive  powder. 

Boron  is  amorphous,  infusible,  insoluble  in  water.  When  it  is 
heated  in  the  air  or  in  oxygen,  it  takes  fire  and  burns  to  boric 
oxide.  It  is  one  of  the  few  elements  which  combine  directly  with 
nitrogen  :  at  a  red  heat  in  an  atmosphere  of  nitrogen  it  is  con- 
verted into  boron  nitride,  BN.  It  also  burns  in  nitrogen  dioxide 
when  heated  in  that  gas,  and  forms  a  mixture  of  boron  nitride  arid 
boric  oxide. 

211.  Boric  Oxide. — Boric  oxide,  of  which  we  have  already 
learned  the  manner  of  formation,  is  a  hard,  transparent,  glass-like 
substance.     It  melts  at  a  red  heat,  and  when  melted  has  the  prop- 
erty of  dissolving  many  metallic  oxides,  which  communicate  vari- 
ous colors  to  the  cooled  oxide.      We  heat  to  redness  the  end  of  a 


138  LESSONS    IN    CHEMISTRY. 

small  platinum  wire,  and,  when  it  is  very  hot,  we  dip  it  into  some 
boric  acid  or  powdered  boric  oxide ;  on  again  heating  this  in  the 
flame,  it  melts  to  a  sort  of  glass  bead,  which  is  perfectly  trans- 
parent and  colorless  when  cold.  We  now  dip  it  into  a  solution 
of  cobalt  chloride,  and  again  heat  it  :  when  it  cools,  the  bead  has 
a  blue  color.  This  blue  color  is  given  by  the  cobalt.  As  many 
metals  give  peculiar  colors  to  such  beads  of  boric  oxide,  we  have 
in  that  substance  a  valuable  reagent  to  aid  in  the  detection  of  the 
metals. 

Boric  oxide  is  not  reduced  by  heating  it  with  charcoal,  but 
when  chlorine  is  passed  over  a  red-hot  mixture  of  boric  oxide  and 
charcoal,  carbon  monoxide,  CO,  is  disengaged,  together  with  the 
vapor  of  a  very  volatile  liquid,  boron  chloride,  BC13. 

B2Q3        +        80        +        301*        =        2BC13        +        SCO 
Boric  oxide.  Boron  chloride. 

212.  When  boric  oxide  is  melted  with  the  metal  aluminium,  a 
part  of  the  metal  is  oxidized,  and  another  part  combines  with  the 
boron  from  which  the  oxygen  was  removed ;  there  is  so  formed  a 
complex  compound  of  boron  and  aluminium,  which  separates  in 
small  crystals  when  the  mass  cools.     As  these  crystals  are  mixed 
with  the  excess  of  solid  aluminium,  we  must  remove  that  metal 
by  boiling  in  dilute  hydrochloric  acid.     Small  octahedral  crystals 
remain  undissolved  :  they  were  long  regarded  as  crystallized  boron. 
Their  composition  is  not  always  the  same.     Their  color  is  yellow, 
red,  or  black :  their  density  is  about  2.6,  and  they  are  almost  as 
hard  as  diamond :  they  will  scratch  rubies,  and  have  sometimes 
been  employed  for  polishing  precious  stones. 

213.  Boric  Acid  and  Borates, — We  have  already  seen  that 
boric  acid  may  be  formed  by  the  action  of  sulphuric  acid  on  borax. 
It  dissolves  in  about  twenty-five  times  its  weight  of  cold  water,  and 
the  solution  is  not  very  strongly  acid ;  it  changes  blue  litmus  to  a 
wine  color. 

It  is  found  in  nature  in  the  craters  of  some  volcanoes.  In  nu- 
merous localities  in  Tuscany  gases  issue  from  cracks  in  the  earth, 
and  these  volcanic  gases  contain  boric  acid.  To  obtain  this  body 


BORIC    ACIDS. — BORAX.  139 

tie  gas  is  caused  to  bubble  through  the  water  of  little  lakes,  and 
when  the  water  is  evaporated,  the  boric  acid  is  left. 

Boric  acid  is  tribasic :  when  it  is  heated  to  100°,  it  is  decom- 
posed into  water  and  metaboric  acid. 

H3B03  HBO2  +          H20 

Boric  acid.  Metaboric  acid. 

If  the  latter  be  heated  to  140°  for  a  time,  it  is  further  decom- 
p  ised  into  another  acid,  called  tetraboric. 

4HB02  H2B*07         +         H20 

Metaboric  acid.          Tetraboriu  acid. 

Tetraboric  acid  is  that  to  which  correspond  borax  and  the 
c  >ujmon  borates.  In  borax,  which  is  sodium  tetraborate,  both  of 
the  hydrogen  atoms  are  replaced  by  sodium. 

214.  BORAX,  Na'2B40T,  was  for  a  long  time  obtained  princi- 
}  illy  from  Asia  and  from  the  boric  acid  of  Tuscany,  but  within 
r  :cent  years  it  has  been  found  in  large  quantities  in  certain  lakes 
(  Borax  Lake,  Lake  Clear)  in  California.  The  lakes  are  dredged, 
a  id  the  mud  from  the  bottom  is  boiled  with  water ;  the  borax 
s  :paratcs  in  crystals  when  the  solution  is  evaporated.  When  a 
v?ry  concentrated  solution  of  borax  cools,  it  deposits,  between  79° 
a  id  56°,  octahedral  crystals  in  which  one  molecule  of  borax  is 
c  tmbined  with  five  molecules  of  water  of  crystallization ;  but 
balow  56°  it  deposits  prismatic  crystals  containing  ten  molecules 
of  water.  As  a  given  quantity  of  borax  will  yield  a  much  heavier 
weight  of  the  latter  crystals  than  of  the  former,  the  prismatic 
crystals  are  those  prepared  for  commerce.  Prismatic  borax  dis- 
solves in  twelve  times  its  weight  of  cold,  or  twice  its  weight  of 
boiling  water. 

When  borax  is  heated,  it  loses  its  water  of  crystallization  more 
quickly  than  that  water  can  evaporate ;  the  borax  is  consequently 
dissolved  in  the  separated  water :  it  is  said  to  melt  in  its  water  of 
crystallization.  As  the  water  is  driven  off  by  the  heat,  it  causes 
the  borax  to  swell  up,  until  it  becomes  a  dry,  white,  and  very 
light  mass.  When  this  is  still  further  heated,  it  melts  to  a  sort  of 
glass,  which  possesses  the  same  property  of  dissolving  metallic 
oxides  that  we  noticed  in  fused  boric  oxide.  For  this  reason  borax 


140  LESSONS    IN    CHEMISTRY. 

is  often  used  in  analysis  instead  of  boric  oxide.  Because  borax 
dissolves  metallic  oxides,  it  is  useful  in  brazing  and  welding.  The 
surfaces  of  metal  to  be  welded  together  become  oxidized  at  the 
high  temperature  necessary,  and  the  oxide  would  prevent  their 
union  :  a  little  borax  sprinkled  on  the  hot  surfaces  dissolves  the 
oxide,  and  the  liquid  is  squeezed  out  when  they  are  pressed 
together,  leaving  clean  surfaces  which  readily  unite. 

215.  We  dissolve  in  alcohol  a  little  boric  oxide,  or  some  borax 
to  which  a  few  drops  of  sulphuric  acid  have  been  added.  On 
lighting  this  alcohol,  it  burns  with  a  green  flame.  This  test  helps 
us  to  recognize  boric  acid  or  a  borate. 


LESSON    XXVII. 
SILICON.     Si  =  28. 

216.  Silicon  is  one  of  the  most  abundant  elements.  In  the 
form  of  oxide  it  exists  in  silica,  or  quartz,  and  it  forms  part  of 
nearly  all  rocks  and  minerals.  It  is  not  easily  obtained  in  the  free 
state,  but  it  can  be  prepared  in  two  forms,  as  an  amorphous  brown 
powder  and  as  dark-gray  octahedra.  It  has  a 
strong  affinity  for  oxygen,  and  is  always  found 
combined  with  that  element  in  nature. 

217.  Silicic  Oxide,  SiO2. — This  compound, 
generally  called  silica,  is  found  in  many  forms. 
Crystallized,  it  constitutes  the  various  kinds  of 
quartz,  such  as  rock  crystal  and  amethyst ; 
amorphous,  it  forms  agate,  flint,  carnelian,  chal- 
cedony. Sandstones  and  sand  are  also  silica. 
When  it  is  not  colorless,  the  colors  are  due  to 
PicT  66  small  quantities  of  metallic  oxides.  Eock- crys- 

tal is  pure  silicic  oxide.  It  forms  hexagonal 
prisms  terminated  by  six-sided  pyramids,  and  the  angles  are  often 
curiously  modified  (Fig.  66).  The  density  of  silica  is  about  2.6. 


SILICA. — GLASS.  141 

Ii:  is  insoluble  in  water ;  infusible  except  in  the  flame  of  the 
o^yhydrogen  blow-pipe,  and  then  only  imperfectly.  It  is  not 
deoxidized  by  reducing  agents,  such  as  hydrogen  and  carbon,  even 
a  the  highest  temperatures.  It  is  scarcely  affected  by  any  chem- 
ical  agents  at  ordinary  temperatures,  with  the  exception  of  hydro- 
fluoric  acid  (§  93).  When  it  is  strongly  heated  with  alkaline 
1  ydrates  or  carbonates,  it  enters  into  combination  with  the  metal, 
1  irming  silicates,  and  these  silicates  are  capable  of  dissolving  silica 
ii  very  high  temperatures.  When  the  mass  cools,  it  constitutes 
i  lass,  and  the  properties  of  the  glass  depend  upon  the  proportions 
c  f  silica  and  alkaline  hydrate  or  carbonate  employed.  If  there 
1  e  a  large  proportion  of  the  alkali,  the  glass  is  soluble  in  water, 
ii  ad  soluble  glass  is  made  by  fusing  silica  with  either  potassium  or 
fc  )dium  carbonate, — generally  the  latter,  because  it  is  cheaper.  The 
;-  )lution  of  this  substance  hardens  as  the  water  evaporates,  and  is 
<  inployed  as  a  cement  and  in  making  artificial  stone. 

218.  Ordinary  glass  is  made  by  melting  in  large  clay  pots,  or 
i  i  furnaces  of  peculiar  construction,  a  mixture  of  fine  white  sand, 
.« )dium  carbonate,  and  lime.     If  it  is  desired  that  the  glass  shall 
not  soften  at  a  high  temperature,  potassium  carbonate  is  used  in- 
s  ead  of  sodium  carbonate.    When  the  bubbles  of  carbon  dioxide, 
v  hich  are  given  off  from  the  carbonate  employed,  have  escaped 
from  the  pasty  liquid,  the  workman  takes  out  some  of  the  molten 
metal,  as  it  is  called,  on  the  end  of  a  long  iron  tube,  through  which 
he  blows  air  into  this  lump  of  soft  glass  ;  if  the  lump  be  in  a 
battle- mould,  the  glass  takes  the  form  of  the  mould.     Common 
window-glass  is  made  by  blowing  large  globes  which  are  drawn 
out  into  cylinders  by  their  own  weight  as  they  hang  on  the  blow- 
pipe.    The  cylinders  when  cold  are  cut  open  their  whole  length, 
a  ad  are  then  heated  in  a  furnace,  and  when  soft  enough  are  unrolled 
into  sheets. 

219.  CRYSTAL,   the  very  heavy  and   perfectly  colorless  glass 
from  which  cut-glass  objects  are  made,  contains  lead  silicate,  which 
ih  formed  by  adding  red  lead  to  the  mixture  of  alkaline  carbonate 
and  sand  before  fusing  it.      A  little  lead  is  often  used  in  making 
common  glass.     The  dark-green  color  of  bottle-glass  is  caused  by 


142  LESSONS    IN    CHEMISTRY. 

the  presence  of  iron  in  the  sand  used,  and,  in  general,  colored 
glasses  owe  the  color  to  the  presence  of  certain  metals,  as  we  shall 
in  time  learn.  Plate-glass  is  cast  on  polished  metallic  tables,  and 
while  still  soft  is  rolled  out  by  heavy  rollers,  as  dough  is  rolled. 
It  is  afterwards  ground  flat  and  polished  by  machinery.  Tumblers, 
goblets,  and  like  objects  are  made  by  pressing  the  soft  glass  into 
moulds. 

220.  By  the  action  of  energetic  acids  the  alkaline  metal  is  at 
once  removed  from  soluble  glass.  We  pour  into  a  saucer  some 
thick  solution  of  sodium  silicate  (sodium  soluble  glass),  and  on 
the  surface  of  this  we  carefully  pour  some  hydrochloric  acid ;  on 
pouring  these  liquids  from  a  little  height  into  another  saucer,  as 
they  run  out  they  mix  on  the  edge,  and  the  silica  which  is  sepa- 
rated from  the  sodium  hangs  on  the  saucer  in  long  icicle-like 


In  a  beaker  glass  we  make  a  rather  dilute  solution  of  sodium 
silicate,  and  gradually  mix  it  with  dilute  hydrochloric  acid.  Here 
also  sodium  chloride  is  formed  by  the  action  of  the  hydrochloric 
acid,  but  no  silica  is  precipitated.  Where  is  it?  It  must  be  in 
the  solution,  and  it  exists  there  in  the  form  of  soluble  silicic  acid. 
It  may  be  separated  from  the  sodium  chloride  by  a  process  called 
dialysis ;  the  sodium  chloride  is  a  crystalline  body,  but  silicic  acid 
is  amorphous.  When  a  solution  containing  a  mixture  of  crys- 
talline and  amorphous  bodies  is  put  in  a  dialyser, — which  is  any 
glass- vessel  of  which  the  bottom  is  cut  out  and  replaced  by  a  piece 
of  parchment  paper  firmly  tied  on, — and  the  dialyser  is  placed  in  a 
vessel  of  water,  the  crystalline  substance  passes  through  the  mem- 
brane, while  the  amorphous  body  remains  in  the  interior.  Then 
when  we  pour  our  solution  containing  silicic  acid  into  a  dialyser, 
and  set  the  dialyser  in  a  vessel  of  water,  after  a  time  we  find  the 
silicic  acid  alone  in  the  water  of  the  inner  vessel.  This  acid  prob- 
ably has  the  composition  H4Si04  =  2H20  -j  SiO2.  If  we  set 
aside  for  a  few  days  the  beaker  containing  it,  the  whole  liquid  is 
converted  into  a  jelly.  The  silicic  acid  has  become  an  insoluble 
silicic  hydrate,  H2Si03  =  H20  -f  SiO2. 

221.  Hydrofluosilicic  Acid. — We  have  seen  how  hydrofluoric 


HYDROFLUOSILICIC    ACID. 


143 


arid  attacks  silica  (§  93).  We  put  into  a  glass  flask  an  intimate 
nixture  of  calcium  fluoride  (fluor-spar)  with  fine  quartz  sand  and 
enough  sulphuric  acid  to  make  a  creamy  liquid.  We  have  adapted 


tube  and  a  delivery- 
of  a  tall  jar  where  it 


FlG.  67. 


U  our  flask  a  cork  having  a  safety- 
tube  which  may  pass  to  the  bottom 
d  ps  into  some  mercury.    On 
this  mercury  we  pour  some 
\\uter,  and,  as  our  gas  must 

0  ercome  the  pressure  of  this 
v  liter  and  the  mercury,  we 
}  >ur  a  little  mercury  in  the 
s  fety-tube  (Fig.   67).     We 
now   gently  heat   our   flask, 
a  id  as  each    bubble  of  gas 
\  isses  through  the  mercury 
a  id  touches  the  water,  a  ge- 

1  tinous  deposit  of  silicic  hy- 
(  rate    is   produced;    we  use 
t  ic    mercury  in    order   that 
t  ic    delivery-tube    may   not 

bjcome  stopped  by  this  deposit.  In  the  reaction  which  is  taking 
place,  the  hydrofluoric  acid  which  is  eliminated  from  the  fluor- 
spar and  sulphuric  acid  at  once  acts  upon  the  silica,  forming  silicon 
fluoride,  SiFl4.  This  is  the  gas  which  comes  from  the  flask. 

2CaFl»     +      2H2SO*      +      SiO2     =     2CaSO*    + 

(.'  tlcium  fluoride.  Silicic  oxide. 

• 

When  this  gas  comes  in  contact  with  water,  a  reaction  takes 
place,  in  which  silicic  hydrate,  H2Si03,  is  formed,  together  with  a 
gas  which  dissolves  in  the  water  and  is  called  hydrofluosilicic  acid. 
It  is  a  double  fluoride  of  silicon  and  hydrogen. 

3SiFl*       +       3H2Q       =      H2Si03       +       2fSiFl*.2HFl) 
Silicon  fluoride.  Hydrofluosilicic  acid. 

The  strong  solution  of  this  gas  is  a  highly  acid  liquid,  and  is 
valuable  as  a  test  for  the  metals  potassium  and  sodium,  which  it 
precipitates  from  solutions  of  their  salts.  To  a  solution  of  potas- 
sium nitrate  we  add  some  of  our  filtered  liquid,  and  at  once  an 


2H20     +     SiFl4 

Silicon  fluoride. 


144  LESSONS    IN    CHEMISTRY. 

insoluble  double  fluoride  of  potassium  and  silicon  is  precipitated, 
while  nitric  acid  now  exists  in  the  solution. 

2KN03       +       SiFl4.2HFl       =    '   2HN03         +        SiFl*.2KFl 

Hydrofluosilicic  acid.  Silicopotassium  fluoride. 


LESSON    XXVIII. 
CARBON.    C  =  12. 

222.  When  we  compare  together  a  diamond,  a  piece  of  char- 
coal, and  a  piece  of  graphite  from  a  lead-pencil,  we  would  not 
suppose  that  they  have  many  properties  in  common  ;  much  less 
would  we  think  that  they  are  different  forms  of  the  same  sub- 
stance.    Yet  this  is  the  case.     They  are  only  varieties  of  the  ele- 
ment carbon.     We  do  not  know  how  the  diamond  and  graphite 
have  been  formed  in  the  earth's  crust,  but  we  know  that  many 
modifications  of  charcoal  may  be  formed  by  the  decomposition 
of  various  compounds  of  carbon.     It  is  probable  that  diamonds 
were  formed  in  the  same  manner,  but  under  circumstances  which 
we  have  not  yet  been  able  to  imitate.     We  may  say,  then,  that 
there  are  three  modifications  of  carbon,  two  crystalline  (diamond 
and  graphite),  and  one  amorphous,  under  which  we  must  class  all 
the  varieties  of  coal  and  charcoal. 

223.  DIAMOND. — This  is  the  hardest  of  substances :  it  can  be 
cut  and  polished  only  by  its  own  dust.     It  is  found  crystallized  in 
regular  octahedra  and   forms  of  twelve,  twenty-four,  and  forty- 
eight  faces,  and  the  faces  are  usually  curved   (Fig.  68).     The 
most  highly  prized  varieties  are  perfectly  colorless,  but  the  tints 
vary  through  all  the  shades,  and  some  diamonds  are  black.     Its 
density  is  about  3.5.     It  is  a  bad  conductor  of  heat  and  elec- 
tricity, and  strongly  refracts  light.     When  it  is  strongly  heated 
in  a  vacuum,  it  blackens,  and  is  converted  into  a  sort  of  coke. 
When  strongly  heated  in  oxygen,  it  burns  into  carbon  dioxide. 

224.  GRAPHITE,  or  plumbago,  is  often  called  black  lead.     It 


CARBON.  145 

occurs  in  brilliant  black  masses,  and  sometimes  in  six-sided  plates. 
It  is  soft  enough  to  be  easily  scratched  by  the  finger-nail,  and 
leaves  a  black  mark  on  paper.  Its  density  is  2.2,  and  it  is  a  good 
conductor  of  heat  and  electricity.  It  burns  into  carbon  dioxide 
wl  en  heated  in  air  to  very  high  temperatures.  It  is  not  usually 
perfectly  pure  carbon,  but  contains  one  or  two  per  cent,  of  foreign 


FIG. 


m  itters.  Graphite  is  used  in  lead-pencils,  and  for  the  manufac- 
tu  re  of  crucibles  :  in  the  latter  it  is  powdered  and  mixed  with 
cl  y,  which  binds  together  the  graphite. 

225.  The  other  varieties  of  carbon  are  amorphous. 

ANTHRACITE  is  a  hard  and  brittle  substance,  containing  from 
ei:;ht  to  ten  per  cent,  of  earthy  matters,  and  sometimes  even 
more. 

BITUMINOUS  COAL  is  softer  and  lighter  than  anthracite.  It 
contains  from  75  to  90  per  cent,  of  carbon,  with  which  is  com- 
bined a  varying  proportion  of  hydrogen.  It  is  the  remains  of 
vegetable  substances  which  were  buried  in  the  earth  in  the  early 
geological  ages.  When  it  is  strongly  heated  out  of  contact  with 
the  air,  various  compounds  of  hydrogen  and  carbon  are  formed, 
together  with  some  water  and  ammonia.  Certain  of  these  com- 
pounds of  carbon  and  hydrogen  are  gases,  and,  since  they  contain 
only  combustible  elements,  they  are  themselves  combustible. 

We  introduce  some  fragments  of  bituminous  coal  into  a  small 
glass  retort,  to  the  beak  of  which  we  have  adapted  a  little  jet 
(Fig.  69).  When  we  heat  the  retort  by  a  flame,  heavy  vapors  are 
disengaged  from  the  coal  ;  some  of  them  condense  in  the  neck  of 
the  retort,  but  those  which  are  gaseous  at  ordinary  temperatures 
Q  k  tl3 


146 


LESSONS    IN    CHEMISTRY. 


pass  out  at  the  jet,  and  when  we  apply  a  flame  they  burn  with  a 
bright  light.  This  is  precisely  the  operation  which  is  conducted 
for  the  manufacture  of  illuminating 
gas  from  bituminous  coal.  The  coal 
is  heated  in  clay  or  iron  retorts  (Fig. 
70),  and  the  liquid  products  are  con- 
densed by  passing  through  a  cold  pipe  ; 
since  coal  always  contains  sulphur  and 
nitrogen,  some  hydrogen  sulphide  and 
~  ammonia  are  formed,  and  these  must  be 

separated  from  the  gas,  for  their  com- 
bustion would  render  the  air  of  a  room  quite  unwholesome.  They 
are  removed  by  passing  the  gas  through  a  tall,  upright  pipe  in 


A,  retorts.  B,  hydraulic  main  for 
condensation  of  liquid  products. 
C,  scrubbers,  in  which  gas  is  washed  with 
water-spray.  D,  litne-purifier.  E,  gas- 
holder. 


FIG.  70. 


which  little  jets  of  water  are  playing,  and  the  ammonia  and  hy- 
drogen sulphide  are  in  great  part  dissolved ;  the  gas  is  still  further 
purified  from  sulphur  by  passing  through  slaked  lime,  and  it  is  then 
conducted  into  large  gas-holders,  from  which  it  passes  into  the  pipes 


CARBON.  147 

for  consumption.  The  liquid  which  first  condenses  from  the  gas 
separates  into  two  layers ;  one  is  an  impure  solution  of  ammonia, 
and,  together  with  the  water  used  for  washing  the  gas,  forms  the 
source  of  the  ammonia  of  commerce  ;  the  other  is  tarry,  and  con- 
tiins  numerous  liquid  and  solid  compounds  of  carbon  and  hydrogen, 
v  Inch  we  must  study  at  another  time.  The  black  substance  which 
remains  in  the  clay  retorts,  as  it  does  in  our  glass  retort,  is  coke. 
As  some  of  the  compounds  of  hydrogen  and  carbon  which  are 
I  ^rmed  are  decomposed  by  the  high  temperature  of  the  retorts, 
these  vessels  become  lined  with  the  carbon,  which  separates,  and 
1  )rms  a  dense,  hard,  strong,  and  sonorous  layer.  It  is  called  gas 
<  arbon,  and  is  used  for  the  carbon  plates  of  voltaic  batteries  and 
i  :>r  the  carbon  electrodes  in  the  electric  light. 

The  minerals  lignite  and  jet,  of  which  ornaments  are  made,  are 
\  arieties  of  bituminous  coal. 

226.  CHARCOAL  is  derived  both  from  wood  and  from  animal 
i  latters.  Wood-charcoal  was  -formerly  made  by  closely  piling  the 
^  rood  and  covering  the  pile  with  earth,  some  holes  being  left  for 
t-ie  admission  of  air.  The  combustion  of  part  of  the  wood  then 
j  reduces  sufficient  heat  to  convert  the  rest  into  charcoal,  or  car- 
\  onize  it.  This  process  is  very  wasteful :  not  only  is  a  large  quan- 
t  ty  of  wood  unnecessarily  burned,  but  the  many  other  products, 
tir,  acetic  acid,  and  wood  alcohol,  which  might  be  obtained,  are 
lost.  Another  process  is  now  being  everywhere  adopted,  in  which 
tie  wood  is  heated  in  iron  retorts,  and  the  vapors  given  off  are 
passed  through  pipes  surrounded  by  other  pipes  through  which 
fiows  a  stream  of  cold  water;  the  liquid  products  are  thus  con- 
densed, and  the  gases  are  conducted  under  the  retort  (Fig.  71). 
The  gas  from  one  retort  is  sufficient  to  carbonize  the  wood  in 
another,  so  that  after  starting  the  operation  little  or  no  fuel  is 
required  and  nothing  is  lost. 

Charcoal  is  brittle  and  sonorous;  its  density  is  about  1.5.  It 
is  a  poor  conductor  of  heat  and  electricity.  It  is  not  pure  carbon  : 
its  combustion  leaves  one  or  two  per  cent,  of  earthy  matter,  prin- 
cipally the  carbonates  of  potassium  and  calcium. 

ANIMAL  CHARCOAL  is  made  by  strongly  heating  waste  horn, 


148 


LESSONS    IN    CHEMISTRY. 


bone,  blood,  hide,  and  other  animal  matters,  in  closed  vessels. 
When  made  from  bone,  it  is  called  bone-black  or  ivory -black :  it 


FIG.  71. 

then  naturally  contains  the  mineral  matters  of  the  bones,  calcium 
phosphate  and  carbonate.  These  may  be  dissolved  out  by  wash- 
ing the  bone-black,  first 
with  hydrochloric  acid, 
and  afterwards  with 
water ;  it  is  then  called 
purified  animal  char- 
coal. 

LAMP-BLACK,  so 
much  used  for  the  manu- 
facture of  printing-ink, 
india-ink,  and  black 
paint,  is  made  by  burn- 
ing oil,  turpentine,  or 
rosin  in  an  insufficient 
supply  of  air.  The 
operation  is  conducted 

in  a  small    furnace  of 
FIG.  72.  ,  .  ,         ,          .. 

which      the      chimney 

opens4litp  a  room  on  whose  walls  the  thick  smoke  of  lamp-black 
settles.     GfefrSfally  these  walls  are  hung  with  canvas,  from  which 


CARBON.  149 

the  lamp-black  is  removed  by  a  conical  scraper  which  can  be 
lowered  by  a  rope  passing  over  a  pulley  (Fig.  72).  Lamp-black 
is  a  fine  powder,  and  usually  contains  oily  and  tarry  matters  from 
the  rosin  :  it  may  be  purified  by  heating  it  red  hot  in  a  covered 
crucible. 

227.  Properties  of  Charcoal. — In  addition  to  the  peculiari- 
ties of  each  variety  which  we  have  considered,  all  of  the  forms  of 
charcoal  are  exceedingly  porous,  and  they  are  able  to  absorb  many 
times  their  volume  of  certain  gases.  We  fill  a  rather  wide  glass 
tube  with  mercury,  and,  after  inverting  it  in 
a  vessel  of  mercury,  we  pass  into  it  some  am- 
monia gas,  made  by  boiling  a  little  ammonia- 
water  in  a  flask.  Now  we  heat  a  piece  of 
charcoal  red  hot,  to  drive  out  all  of  the  gases 
which  it  has  absorbed  from  the  air,  and  we 
push  it  under  the  mercury  into  the  tube 
(Fig.  73).  It  rises  to  the  surface,  and  in- 
stantly we  see  the  volume  of  ammonia  dimin- 
ishing ;  the  gas  is  being  absorbed  by  the 
charcoal,  and  after  we  remove  the  latter  from 
the  tube  we  will  find  it  much  heavier,  and 
having  a  strong  odor  of  ammonia.  Charcoal 
will  absorb  about  ninety  times  its  volume  of  ammonia,  fifty-five  of 
hydrogen  sulphide,  and  large  quantities  of  most  other  gases.  It 
absorbs  less  than  twice  its  volume  of  hydrogen,  and  about  eight 
times  its  volume  of  either  carbon  monoxide,  oxygen,  or  nitrogen. 
These  gases  are  driven  out  when  the  charcoal  is  heated.  We  can 
now  understand  that  in  some  cases  charcoal  is  an  excellent  disin- 
fectant :  if  a  dead  mouse  or  other  small  animal  be  buried  in  a  box 
of  powdered  charcoal,  it  will  be  found  after  some  weeks  to  have 
dried  up,  and  the  charcoal  will  have  absorbed  all  of  the  unpleasant 
odors.  Charcoal  has  also  the  property  of  absorbing  many  color- 
ing matters  in  its  pores,  where  they  are  probably  oxidized  :  animal 
charcoal  possesses  this  property  in  the  most  marked  degree.  We 
pour  some  litmus  solution  into  a  filter  containing  animal  charcoal, 
and  the  liquid  passes  through  colorless.  This  peculiarity  renders 

13* 


150  LESSONS    IN    CHEMISTRY. 

animal  charcoal  valuable  for  decolorizing  many  liquids,  and  enor- 
mous quantities  of  it  are  employed  for  decolorizing  sugar.  The 
brown  color  is  removed  from  crude  sugar  by  dissolving  it  in  water 
and  filtering  the  syrup  through  animal  charcoal.  An  excellent 
filter  for  the  purification  of  drinking-water  consists  of  a  layer  of 
charcoal  between  two  layers  of  sand  :  the  charcoal  must  be  changed 
from  time  to  time,  or  it  may  be  removed  and  heated  red  hot  in  a 
covered  vessel ;  it  is  then  again  fit  for  use. 

228.  The  strongest  affinity  of  carbon  is  for  oxygen,  but  this 
affinity  is  not  manifested  at  ordinary  temperatures.  When,  how- 
ever, the  temperature  is  raised  to  redness  and  the  combustion  of 
charcoal  begins,  sufficient  energy  is  developed  by  the  chemical 
action  to  keep  the  temperature  at  the  combining  point,  and  the 
oxidation  goes  on  without  further  aid.  The  product  of  the  com- 
bustion of  carbon  in  air  or  in  oxygen  is  carbon  dioxide,  CO2.  Be- 
cause of  its  strong  affinity  for  oxygen,  charcoal  can  remove  that 
element  from  various  oxidized  bodies  :  it  is  a  reducing  agent.  We 
have  already  seen  an  example  of  this  reduction  when  we  heated 
charcoal  with  cupric  oxide  (§  13).  When  such  a  reduction  re- 
quires a  temperature  about  redness,  carbon  dioxide  is  formed,  and 
this  was  the  case  with  cupric  oxide  and  charcoal. 

2CuO         +         C        =         Cu2         +         CO2 
Cupric  oxide.  Copper.         Carbon  dioxide. 

When,  however,  the  reduction  requires  a  white  heat,  or  near 
that  temperature,  carbon  monoxide,  CO,  is  formed.  This  is  the 
action  of  charcoal  on  zinc  oxide. 

ZnO         +         C        =  CO  +         Zn 

Zinc  oxide.  Carbon  monoxide. 


LESSON    XXIX. 
OXIDES   OP   CARBON. 

229.  Carbon  Monoxide,  CO. — This  gas  might  be  made  by 
heating  to  whiteness  in  clay  retorts  a  mixture  of  zinc  oxide  and 
charcoal,  but  this  would  require  a  furnace  and  be  inconvenient. 


CARBON    MONOXIDE. 


151 


We  can  prepare  the  gas  more  conveniently  by  heating  in  a  glass 
flask  a  mixture  of  oxalic  and  strong  sulphuric  acids.  The  oxalic 
icid,  which  is  a  compound  of  carbon,  oxygen,  and  hydrogen,  is 
then  decomposed  into  carbon  monoxide,  carbon  dioxide,  and  water. 
C20*H2  CO2  +  CO  +  H20 

Oxalic  acid.  Carbon  dioxide.        Carbon  monoxide. 

The  water  will  be  retained  by  the  sulphuric  acid,  but  we  must  pass 
the  gases  through  a  bottle  containing  a  solution  of  sodium  hydrate, 
by  which  the  carbon  dioxide  will  be  absorbed.  Sodium  carbonate 
is  formed  in  the  bottle,  and  we  collect  the  carbon  monoxide  over 
water  (Fig.  74). 


FIG 


230.  Carbon  monoxide  is  a  colorless,  odorless  gas.  Its  density 
compared  to  air  is  0.967,  or  compared  to  hydrogen,  14.  It  is  in- 
soluble in  water.  It  is  very  poisonous  :  when  it  is  taken  into  the 
lungs  it  combines  with  the  red  globules  in  the  blood,  and  prevents 
them  from  carrying  into  the  system  the  oxygen  which  is  necessary 
for  the  processes  of  life  (§  33). 


152  LESSONS    IN    CHEMISTRY. 

Just  as  we  made  a  similar  experiment  with  hydrogen,  carefully 
we  lift  our  jar  from  the  water,  and  push  into  it  a  lighted  taper. 
The  gas  takes  fire  and  burns  with  a  blue  flame  at  the  mouth  of 
the  jar,  but  the  taper  is  extinguished.  Carbon  monoxide  will  not 
support  combustion,  but  it  will  combine  with  oxygen  to  form  carbon 
dioxide. 

It  is  interesting  here  to  study  the  amount  of  heat  disengaged  by  the  com- 
bustion of  carbon.  Naturally,  we  can  understand  that  when  a  given  weight 
of  charcoal  is  burned,  a  fixed  quantity  of  heat  will  be  developed,  enough  to 
raise  a  certain  weight  of  water,  let  us  say,  from  0°  to  1°.  When  this  same 
weight  of  charcoal  is  converted  into  carbon  monoxide,  the  combustion  of  the 
latter  gas  will  not  heat  as  much  water  through  the  same  temperature.  What 
has  become  of  the  energy  which  has  disappeared  from  the  charcoal?  It  must 
have  been  lost  from  the  atom  of  carbon  and  the  first  atom  of  oxygen  wjth 
which  it  combined.  Many  careful  experiments  have  shown  that  this  is  the 
case,  and  that  the  same  quantity  of  carbon  always  develops  the  same  quan- 
tity of  heat  when  it  is  converted  into  carbon  dioxide,  whether  it  is  so  con- 
verted at  once,  or  whether  it  first  forms  carbon  monoxide  and  this  combines 
with  an  additional  atom  of  oxygen.  We  so  have  a  method  which  enables  us 
to  determine  the  heat  or  energy  of  formation  of  bodies  like  carbon  monoxide. 
For  if  from  the  amount  of  energy  developed  by  the  conversion  of  a  certain 
amount  of  carbon  into  carbon  dioxide,  we  subtract  that  which  is  developed  by 
the  combustion  of  a  quantity  of  carbon  monoxide  containing  the  same  weight 
of  carbon,  we  will  have  the  energy  with  which  one  atom  of  carbon  combines 
with  one  atom  of  oxygen.  In  making  such  determinations,  a  number  of 
grammes  of  the  substance  is  taken  which  would  express  the  atomic  weight  if 
one  atom  of  hydrogen  weighed  one  gramme  ;  and  the  result,  which  is  expressed 
in  the  number  of  kilogrammes  of  water  which  would  be  raised  from  0°  to  1° 
by  the  heat  produced,  is  called  the  heat  of  formation  of  the  compound. 

231.  Carbon  monoxide  is  formed  by  the  action  of  carbon  dioxide 
on  carbon  at  very  high  temperatures. 

CO2     +     C     =     2CO 

When  fresh  coal  is  thrown  on  a  hot  fire,  the  escape  of  the  carbon 
dioxide  from  the  burning  coal  is  retarded,  and  that  gas  remains 
in  contact  with  the  coal  long  enough  to  be  partially  reduced  to 
carbon  monoxide.  The  latter  then  occasions  the  blue  flame  with 
which  we  are  all  familiar.  Carbon  monoxide  has  the  property  of 
passing  through  the  pores  of  red-hot  iron,  and  it  often  so  escapes 
through  the  iron  of  stoves  which  are  not  properly  lined  with  fire- 
brick ;  fortunately,  the  gas  formed  from  coal  has  a  decided  odor, 


CARBON    DIOXIDE.  153 

usually  due  to  the  sulphur  in  the  coal,  and  this  odor  generally 
makes  us  aware  of  the  presence  of  the  poisonous  gas. 

232.   When  steam  is  passed  over  hot  coal  or  charcoal,  a  mixture 
of  carbon  monoxide  and  hydrogen  is  formed. 
C    +    H20    =    CO    +    H2 

When  this  mixture  is  passed  through  volatile  compounds  of 
iiydrogen  and  carbon,  such  as  we  shall  learn  are  contained  in  the 
ighter  kinds  of  petroleum,  the  gases  become  charged  with  the 
sapors  of  those  compounds :  if  they  then  be  passed  through  hot 
pipes,  various  gaseous  compounds  of  carbon  and  hydrogen  are 
conned,  and  these  burn  with  light-giving  flames.  The  water-gas 
ised  for  illumination  in  some  cities  is  manufactured  in  this  manner. 

233.  CARBOXVL  CHLORIDE. — Carbon  monoxide  combines  directly  with  chlo- 
-ine  when  a  mixture  of  the  two  gases  is  exposed  to  direct  sunlight,  and  a 
suffocating  gas,  whose  molecule  contains  COC12,  is  formed.  The  carbon  mon- 
>xide  acts  as  a  radical,  just  as  sulphur  dioxide  in  sulphuryl  chloride,  S02CI2, 
ind  this  radical  is  called  carbonyl.  Like  sulphuryl  chloride,  carbonyl  chlo- 
ride reacts  with  water,  and  in  so  doing  it  yields  carbon  dioxide  and  hydro- 
chloric acid. 

COC12     +     H20     =     CO2     +     2HC1 

234.  Carbon  Dioxide,  CO2.— In  a  gas-bottle,  like  that  which 
we  used  for  preparing  hydrogen  (Fig.  75),  we  put  some  water  and 

broken  marble,  and  pour  hydro- 
chloric acid  through  the  funnel- 
tube.  As  the  gas  with  which 
we  wish  to  experiment  is  very 
heavy,  we  collect  it  by  down- 
ward dry  displacement,  passing 
the  end  of  our  delivery-tube  to 
the  bottom  of  the  jar.  When 
the  effervescence  in  the  bottle 
has  continued  for  a  moment, 
we  put  a  lighted  taper  into  the 
j,  *g  jar  in  which  we  are  collecting 

the  gas :  the  flame  is  at  once 

extinguished.  The  jar  is  full  of  carbon  dioxide,  and  for  such 
substances  as  the  matter  of  the  taper  the  oxygen  in  this  gas 


154  LESSONS   IN   CHEMISTRY. 

has  exhausted  its  energy  in  combining  with  the  carbon :  it  will 
unite  with  no  more.  In  our  gas-bottle  we  have  formed  water  and 
calcium  chloride,  for  marble  is  calcium  carbonate. 

CaCO3       +        2HC1        =         CaCl2         +       H20      +      CO2 
Calcium  carbonate.  Calcium  chloride. 

235.  Carbon  dioxide  is  a  colorless  gas  ;  it  has  a  faint  but  some- 
what pungent  odor  and  taste.      Its  density  compared  to  air  is 
1.529,  or  compared  to  hydrogen,  22.     We  balance  on  a  scale-pan 
an  open  and  erect  paper  bag,  into  which  we  quickly  pour  the  car- 
bon dioxide  from  our  jar  :  the  descending  pan  at  once  shows  us 
that  the  gas  is  heavier  than  the  air  which  it  displaces.     At  0°,  it 
is  converted  into  a  colorless  liquid  by  a  pressure  of  thirty-six  at- 
mospheres, and  when  the  liquid  is  allowed  to  evaporate  rapidly, 
it  absorbs  so  much  heat  in  assuming  the  gaseous  state  that  the 
temperature  falls  to  — 78°,  and  a  part  of  the  carbon  dioxide  is 
frozen  to  a  snow-like  mass.     When  touched,  this  solid  produces  a 
burn  like  fire,  for   the  life  of  animal  tissues  cannot  continue  at 
such  low  temperatures. 

Carbon  dioxide  is  soluble  in  its  own  volume  of  water,  and  the 
quantity  of  the  gas  which  can  be  absorbed  by  a  givei  quantity  of 
water  is  directly  proportional  to  the  pressure :  if  the  pressure  be 
doubled,  twice  as  much  gas  will  be  dissolved,  etc.  We  know, 
however,  that  by  a  double  pressure  two  volumes  of  any  gas  will 
be  reduced  to  one  volume  (Mariotte's  law)  :  hence  we  may  say 
that  water  always  dissolves  its  own  volume  of  carbon  dioxide,  no 
matter  what  the  pressure.  When  the  pressure  is  diminished  or. 
removed,  the  gas  escapes  with  effervescence,  until  the  volume 
remaining  dissolved  is  equal  to  that  of  the  water.  The  beverage 
generally  known  as  gaseous  water  or  soda-water,  is  simply  water 
into  which  about  five  times  its  volume  of  carbon  dioxide  has  been 
pumped. 

236.  We  have  already  seen  that  carbon  dioxide  neither  burns 
nor  supports  combustion,  and  a  simple  experiment  shows  us  its 
power  of  extinguishing  burning  bodies,  at  the  same  time  that  we 
will  be  reminded  of  its  weight.     We  fix  a  short  taper  or  piece  of 
candle  in  a  cork,  and,  after  lighting  it,  put  it  in  a  small  jar  into 


CARBON    DIOXIDE. 


155 


which  we  pour  the  carbon  dioxide  from  another  jar  which  we  have 
dlled  by  dry  displacement :  the  flame  is  extinguished  as  if  we  had 
poured  water  on  it  (Fig.  76).  Carbon 
dioxide  is  not  poisonous,  but  it  pro- 
duces death  by  suffocation, — that  is, 
exclusion  of  oxygen.  It  collects  in 
wells  and  brewers'  vats,  and  may  then 
oe  detected  by  its  power  of  extinguish- 
^ng  flames  lowered  into  it :  if  there  be 
enough  of  the  gas  present  to  extin- 
guish or  nearly  extinguish  a  flame. 
it  would  not  be  safe  for  a  man  to  enter  __ 
^uch  a  place  before  removing  the  gas,  f| 
which  can  be  done  by  agitating  the 
,iir  so  that  currents  maybe  established. 

237.  Certain  substances  which  have  the  power  of  reducing 
3arbon  dioxide  may  burn  in  the  gas.  Over  a  piece  of  the  metal 
potassium  contained  in  a  glass  bulb,  we  pass  carbon  dioxide  that 

o 


FIG.  76. 


FIG.  77. 


has  been  dried  by  passing  through  a  tube  containing  pumice-stone 
and  sulphuric  acid.  When  we  warm  the  potassium,  it  takes  fire 
and  burns  with  a  red  light,  and  a  deposit  of  charcoal  is  formed 
in  the  bulb  (Fig.  77).  The  potassium  has  reduced  some  of  the 


156  LESSONS    IN   CHEMISTRY. 

carbon  dioxide,  and  has  combined  with  another  portion,  forming 
potassium  carbonate. 

238.  We  pass  a  few  bubbles  of  carbon  dioxide  into  some  lime- 
water  :  the  liquid  quickly  becomes  milky  by  the  formation  of  in- 
soluble calcium  carbonate.  This  test  enables  us  to  recognize  carbon 
dioxide.  Calcium  carbonate  is  insoluble  in  water,  but  if  we  pass 
the  gas  for  a  long  time  through  our  milky  liquid,  the  cloudiness 
disappears ;  water  containing  carbon  dioxide  in  solution  will  dis- 
solve calcium  carbonate.  If,  however,  we  boil  this  liquid  so  that 
all  of  the  dissolved  carbon  dioxide  shall  "be  driven  out,  the  calcium 
carbonate  again  separates,  usually  as  small  crystalline  particles, 
which  settle  as  the  water  cools.  The  stalactites  and  incrustations 
in  caves  are  formed  by  the  drippings  of  water  holding  calcium 
carbonate  in  solution  by  an  excess  of  carbon  dioxide  ;  as  the  gas 
passes  off  gradually  into  the  air,  the  calcium  carbonate  becomes 
insoluble  and  is  deposited. 


LESSON    XXX. 

CARBONATES. 

239.  Carbon  dioxide  corresponds  to  an  acid  which  would  be  formed  by  the 
action  of  one  molecule  of  the  gas  on  one  molecule  of  water.  The  solution  of 
the  gas  in  water  is  feebly  acid,  and  we  may  believe  that  it  contains  carbonic 
acid,  H2C03  =  CO2  f  H20.  Carbon  dioxide  is  often  called  carbonic  anhydride  ; 
anhydride  means  without  water,  and  carbonic  anhydride  thus  signifies  carbonic 
acid  less  the  elements  of  water.  Although  this  acid  cannot  be  separated  from 
the  solution,  for  when  the  water  is  evaporated  carbon  dioxide  is  driven  out, 
there  are  numerous  salts  formed  by  the  replacement  of  one  or  both  of  the 
atoms  of  hydrogen  in  H2C03.  These  salts  are  the  carbonates ;  they  may  be 
easily  recognized  by  the  action  of  hydrochloric  acid,  which  produces  with 
them  an  effervescence  due  to  the  escape  of  carbon  dioxide;  we  may  identify 
this  gas  by  the  milkiness  which  it  produces  in  lime-water. 

There  are  two  classes  of  carbonates;  those  in  which  both  atoms  of  hydrogen 
in  H2C03  are  replaced  by  metal,  and  others  in  which  only  one  of  these  atoms 
is  replaced.  The  latter  are  called  the  acid  carbonates,  or  sometimes  the  dicar- 
bonates.  Carbonic  acid  is,  then,  dibasic. 


SODIUM    CARBONATE.  157 

With  the  exception  of  the  carbonates  of  sodium,  potassium,  and 
ithium,  all  of  the  carbonates  of  the  metals  are  insoluble  in  water: 
;hey  dissolve  slightly,  however,  in  water  containing  carbon  dioxide. 
They  all  effervesce  when  treated  with  hydrochloric  or  sulphuric 
icid,  carbon  dioxide  being  disengaged. 

240.  Sodium  Carbonate,  Na2C03. — Enormous  quantities  of 
:his  salt,  which  is  commonly  called  soda,  or  sal  soda,  are  used  for 
ohe  manufacture  of  glass  and  of  soap,  and  for  the  preparation  of 
the  many  compounds  of  sodium  that  are  used  in  the  arts.  It  is 
usually  manufactured  from  common  salt,  and  the  process  which  is 
Doming  into  general  use  depends  on  a  reaction  between  the  salt 
ind  ammonium  acid  carbonate  (§  251).  We  mix  saturated  solu- 
tions of  ammonium  acid  carbonate  and  sodium  chloride,  and  a  fine 
white  deposit  is  formed  in  the  liquid.  This  is  sodium  acid  car- 
bonate, and  ammonium  chloride  exists  in  the  solution. 

NaCl         +         (NH4)HC03  NH*C1  +         NalICO3 

Sodium  chloride.  Ammonium  acid  Ammonium  chloride.  Sodium  acid 

carbonate.  carbonate. 

This  operation  is  conducted  on  a  large  scale,  and  the  sodium 
acid  carbonate  is  converted  into  sodium  carbonate  by  the  action  of 
heat.  Two  molecules  of  the  acid  carbonate  then  lose  one  molecule 
of  water,  and  one  of  carbon  dioxide. 

2XaHC03  Na2C03  +         H20         +         CO2 

Sodium  acid  carbonate.  Sodium  carbonate. 

The  ammonium  chloride  is  converted  into  ammonia  by  heating 
it  with  lime  (§  136),  and  the  carbon  dioxide  formed  by  heating  the 
sodium  acid  carbonate,  together  with  more  which  is  obtained  from 
the  gases  of  the  furnace-chimneys,  serves  to  convert  the  ammonia 
again  into  ammonium  acid  carbonate. 

NH3     +     H2Q     +     CO2     =     (NH*)HC03 

The  only  waste  product  is,  then,  the  calcium  chloride  left  after 
the  preparation  of  the  ammonia.  In  the  older  process,  which  the 
ammonia-soda  process  is  gradually  replacing,  the  sodium  chloride 
is  first  converted  into  sodium  sulphate  (§  77)  ;  this  is  mixed  with 
chalk  and  coal,  and  the  mixture  heated  by  the  flame  of  a  rever- 
beratory  furnace  (Fig.  78)  yields  a  mixture  containing  calcium 
sulphide  and  sodium  carbonate.  The  last  is  dissolved  out  by  water, 

14 


158 


LESSONS    IN    CHEMISTRY. 


and  the  waste  heat  of  the  furnace  is  employed  not  only  to  evap- 
orate the  solution  obtained  (C  and  D),  but  to  dry  the  mixture  of 
sodium  sulphate,  chalk,  and  coal  (B)  before  introducing  it  into 
the  hottest  part  of  the  furnace  (A).  This  is  named,  from  its 
inventor,  the  Le  Blanc  process. 

Sodium  carbonate  is  also  manufactured  from  the  mineral  cryolite, 
a  double  fluoride  of  sodium  and  aluminium,  of  which  large  quan- 


FIG.  78. 

titles  are  found  in  Greenland.  The  cryolite  is  heated  with  lime, 
and  the  reaction  yields  calcium  fluoride  and  a  compound  known  as 
aluminate  of  sodium :  it  is  a  combination  of  the  oxides  of  sodium 
and  aluminium. 

A1*0*.8N»>0 

Aluminate  of  sodium. 


6CaO     = 

Lime.          Calcium  fluoride. 


A12Fl6.6NaFl 
Cryolite. 

The  aluminate  of  sodium  is  dissolved  from  the  mass  by  water,  and 
carbon  dioxide  passed  through  the  solution  forms  sodium  carbonate, 
while  insoluble  aluminium  hydrate  is  precipitated. 

Al203.3Na20      +     3C02     +     3H20     =  AP(OH)«          +     3Na2C03 

Aluminate  of  sodium.  Aluminium  hydrate. 

The  aluminium  hydrate  is  used  for  the  manufacture  of  alum. 

Sodium  carbonate  forms  large  crystals  containing  ten  molecules 
of  water  of  crystallization  for  one  molecule  of  the  salt.  When  it 
is  exposed  to  the  air,  it  gradually  loses  this  water,  and  falls  to  a 
dry,  white  powder :  it  is  said  to  effloresce.  The  crystals  dissolve 
in  about  four  times  their  weight  of  water  at  20°,  and  the  solution 
has  an  alkaline  reaction  and  an  unpleasant  alkaline  taste.  The 
salt  is  insoluble  in  alcohol. 

241.  Sodium  Acid  Carbonate,  NaHCO3,  is  less  soluble  than 


POTASSIUM     CARBONATE.  159 

the  carbonate,  and  is  precipitated  when  carbon  dioxide  is  passed 
i  hrough  a  saturated  solution  of  the  latter  salt.  It  is  usually  a 
vhite  powder,  which,  when  heated  or  boiled  with  water,  is  decom- 
posed into  water,  sodium  carbonate,  and  carbon  dioxide  which 
-scapes.  It  is  commonly  called  bicarbonate  of  soda,  or  baking- 
-oda;  it  forms  part  of  the  mixtures  known  as  baking-powders, 
.vhich  contain  some  acid  substance  that  may  react  with  the  acid 
•arbonate,  setting  free  carbon  dioxide  in  bubbles  through  the 
lough.  Sodium  acid  phosphate  is  such  a  substance ;  sodium  acid 
•arbonate  may  convert  it  into  either  disodium  or  trisodium  phos- 

ohate. 

NaHCO3     +     NaH2P04     =     Na2HP04     +     H20     +     CO2 

242.  Potassium  Carbonate,  K2C03.— This  compound  is  com- 
monly called  potash,  because  it  was  for  a  long  time  derived  only 
from  wood-ashes ;  it  is  extracted  from  the  ashes  by  causing  water 
to  trickle  through  them,  a  process  which  is  called  lixiviation.  The 
solution  so  obtained  is  evaporated  to  dryness,  and  the  residue 
strongly  heated  in  the  air.  The  potash  of  commerce  contains  only 
from  60  to  80  per  cent,  of  potassium  carbonate.  The  remainder 
consists  of  other  potassium  salts,  principally  the  chloride  and  sul- 
phate :  when  these  are  partially  removed  by  an  imperfect  purifica- 
tion, the  product  is  called  pearl-ash. 

At  Stassfurth,  in  Prussia,  there  are  large  deposits  of  a  double 
chloride  of  potassium  and  magnesium  ;  the  mineral  is  called  Stass- 
furth salt,  and  contains  KCl.MgCP  -f-  6H20.  It  is  decomposed 
by  boiling  with  water,  and,  on  cooling,  potassium  chloride  crys- 
tallizes from  the  liquid,  while  magnesium  chloride  remains  in  the 
solution.  Potassium  carbonate  is  now  manufactured  from  this 
potassium  chloride  by  a  method  similar  to  the  Le  Blanc  process 
for  sodium  carbonate. 

Potassium  carbonate  is  white,  and  dissolves  in  less  than  its  own 
weight  of  water.  It  is  very  alkaline,  and  has  a  burning  taste. 
It  is  deliquescent ;  that  is,  it  attracts  moisture  from  the  air  and 
dissolves  in  the  water  so  absorbed.  It  may  be  obtained  in  crys- 
tals' containing  two  molecules  of  water  by  allowing  a  hot  concen- 
trated solution  to  cool. 


160  LESSONS    IN    CHEMISTRY. 

243.  Potassium  Acid  Carbonate,  KHCO3,  is  prepared,  like 
sodium  carbonate,  by  passing  carbon  dioxide  through  a  solution 
of  potassium  carbonate.     It  is  less  soluble  than  the  latter,  and 
separates  from  the  solution  in  crystals.     Like  sodium  acid  car- 
bonate, it  is  decomposed  by  heat,  whether  it  be  dry  or  in  solu- 
tion. 

244.  Calcium  Carbonate,  CaCO3. — This  substance  is  one  of 
the  most  abundant  of  minerals.     As  calcite,  or  Iceland  spar,  it 
forms  doubly-refracting  rhombohedra :  as  aragonite,  it  is  in  right 
rectangular  prisms.     It  also  constitutes  marble,  limestone,  chalk, 
and  the  greater  part  of  the  matter  of  shells  and  corals.     When 
heated  to  bright  redness  in  open  vessels,  it  is  decomposed  into 
carbon  dioxide  and  lime,  which  is  calcium  oxide. 

245.  Strontium  Carbonate,   SrCO3,   constitutes    the    white 
mineral  strontianite. 

246.  Barium  Carbonate,  BaCO3,  is  found  crystallized  in  nature 
in  the  mineral  witlierite.     The  carbonates  of  calcium,  strontium, 
and  barium  are  precipitated  when  a  solution  of  sodium  or  potas- 
sium carbonate  is  added  to  a  neutral  solution   of  any  calcium, 
strontium,  or  barium  salt. 

247.  Magnesium  Carbonate,  MgCO3,  constitutes  the  minerals 
magnesite  and  giobertite.    Dolomite  is  a  double  carbonate  of  calcium 
and  magnesium  ;  it  is  a  magnesian  limestone.     White  magnesia  is 
a  variable   compound   of  magnesium   carbonate  and  magnesium 
hydrate,  made  by  adding  an  excess  of  sodium  carbonate  solution 
to  a  boiling  solution  of  magnesium  sulphate,  and  drying  the  pre- 
cipitate. 

248.  Zinc  Carbonate,  ZnCO3,  constitutes  the  mineral  calamine, 
an  important  ore  of  zinc. 

249.  Ferrous  Carbonate,   FeCO3,  is  found  native  in  brown 
crystals  as  spathic  iron. 

250.  Lead  Carbonate,  PbCO3,  is  found  crystallized  in  nature. 
It  is  precipitated  as  an  amorphous  white  powder  when  any  soluble 
lead  salt  is  treated  with  sodium  carbonate.     White  lead  is  a  mix- 
ture of  varying  proportions  of  lead  carbonate  and  lead  hydrate. 
It  is  manufactured  by  the  joint   action  of  carbon   dioxide   and 


AMMONIUM    CARBONATES.  161 

vapor  of  acetic  acid  on  metallic  lead.    Acetic  acid,  that  is,  vinegar, 
is  put  into  earthen  pots,  and  the  lead,  either  in  a  rolled  sheet  or 
in  flat  rings,  is  supported  on  little  pro- 
jections above  the  vinegar   (Fig.  79).  ^^^^^^^^^^, 
V  great  number  of  these  pots  are  pre- 
tared,   and  loosely  covered  with  disks 
•>f  lead  (D)  :  they  are  then  arranged  in 
dyers  on  boards,  each  layer  resting  on 
i  bed  of  refuse  bark  from  tanneries,  or 
»f  horse-manure.    These  substances  un- 
lergo  a  sort  of  slow  oxidation,  and  dis- 
•ngage   carbon   dioxide,    which  in    the 

tresence  of  the  acetic  acid  converts  the  surface  of  the  lead  into 
arbonate.  We  may  suppose  that  lead  acetate  is  first  formed,  and 
hat  this  is  at  once  decomposed  by  the  carbon  dioxide,  forming 
ead  carbonate,  while  acetic  acid  is  regenerated.  When  the  greater 
>art  of  the  lead  has  been  so  changed  into  carbonate,  the  pots  are 
•pened  and  the  white  lead  is  scraped  from  the  remaining  metal. 

There  is  another  process,  which  depends  on  the  facility  with 
rhich  lead  acetate  solution  dissolves  lead  oxide,  and  with  which 
t  his  oxide  is  precipitated  as  carbonate  when  carbon  dioxide  is  passed 
through  the  solution.  Lead  acetate  is  then  again  formed  in  the 
solution,  and  is  used  to  dissolve  more  oxide,  which  is  in  its  turn 
precipitated  by  carbon  dioxide. 

Excepting  sodium  carbonate  and  potassium  carbonate,  all  the 
C'ther  salts  which  we  have  just  considered  are  decomposed  by  heat 
into  carbon  dioxide  and  oxide  of  the  metal. 

251.  Ammonium  Carbonates. — The  ammonium  carbonate  of 
commerce  is  commonly  called  a  sesquicarbonate,  and  is  probably  a 
compound  of  several  bodies.  It  is  made  by  subliming  a  mixture 
of  chalk  and  ammonium  sulphate  in  large  retorts.  Its  compo- 
sition is  expressed  by  the  formula  2[(NH*)2C03]  -f-  CO2  -f  H20. 
It  is  a  crystalline  substance,  having  a  strong  ammoniacal  odor 
and  a  sharp,  burning  taste.  It  is  soluble  in  water.  When  it  is 
exposed  to  the  air,  it  gradually  decomposes,  losing  ammonia  and 

leaving  ammonium  acid  carbonate,  NIP.HCO3.     The  latter  body 
I 


162  LESSONS    IN    CHEMISTRY. 

may  also  be  formed  by  passing  carbon  dioxide  into  ammonia-water 
until  no  more  of  the  gas  is  absorbed.  It  then  crystallizes  when 
the  liquid  is  cooled.  Ammonium  carbonate,  (NH4/C03,  separates 
in  crystals  when  the  ammonhrn  carbonate  of  commerce  is  dis- 
solved in  ammonia-water  and  the  solution  is  artificially  cooled. 


LESSON    XXXI. 

COMPOUNDS   OF   CARBON  WITH   SULPHUR  AND 
NITROGEN. 

252.  Carbon  Bisulphide,  CS2. — When  sulphur  vapor  is  passed 
over  red  hot  charcoal  or  coal,  the  two  elements  combine,  forming 
carbon  disulphide,  which  passes  off  as  a  vapor  that  may  be  con- 
densed in  any  suitable  cooling  apparatus.  This  substance  is 
manufactured  by  throwing  sulphur  into  coal  heated  to  redness  in 
inclined  iron  cylinders,  provided  with  openings  for  the  introduction 
of  sulphur  and  the  escape  of  the  vapor. 

It  is  a  colorless  liquid,  having  the  property  of  highly  refracting 
light.  When  pure,  it  has  a  rather  pleasant  odor,  but  the  com- 
mercial product  usually  contains  small  quantities  of  other  com- 
pounds which  communicate  to  the  liquid  a  strong  and  often  dis- 
gusting odor :  it  is  purified  by  distillation  with  lime.  Its  density 
at  15°  is  1.27.  It  is  almost  insoluble  in  water.  It  boils  at  46°. 
It  is  very  inflammable :  we  heat  a  wire  to  redness,  withdraw  it 
from  the  flame,  and  for  some  time  after  it  has  cooled  below  a 
visible  heat  it  will  still  inflame  carbon  disulphide  contained  in  a 
small  dish.  The  vapor  forms  an  explosive  mixture  with  the  air 
or  with  oxygen.  The  products  of  the  combustion  of  carbon  di- 
sulphide are  carbon  dioxide  and  sulphur  dioxide. 
CS2  +  302  =  CO2  +  2S02 

If  a  few  thin  iron  wires  are  held  in  the  flame  of  vapor  of  carbon 
disulphide  which  is  heated  in  a  small  test-tube  provided  with  a 
cork  and  jet,  the  air  and  sulphur  combine,  producing  brilliant 


CARBON    BISULPHIDE. 


163 


sparks  and  molten  globules  of  iron  sulphide,  which  drop  from  the 
ends  of  the  wires  (Fig.  80). 
Carbon  disulphide  is  used 
for  extracting  oil  from  seeds 
;ind  other  matters,  for  it 
'lissolves  fatty  substances 
quickly  and  in  the  cold, 
ind  may  readily  be  distilled 
ind  recovered  from  the  so- 
ution,  leaving  a  much  larger 
quantity  of  oil  than  could 
)Q  extracted  by  pressure. 
It  is  used  in  vulcanizing 
caoutchouc,  an  operation 
.vhich  depends  on  the  com- 
>ination  of  the  caoutchouc  FIG.  80. 

»vith  a  certain   quantity  of 

;ulphur,  as  it  is  able  to  dissolve  not  only  the  caoutchouc  but  the 
-ulphur  chloride  which  is  used  in  the  operation.  We  have  already 
;een  that  carbon  disulphide  dissolves  both  sulphur  and  phosphorus. 

253.  Carbon   disulphide  is  closely  related   to    carbon   dioxide. 
We  have  studied  the  general  composition  of  the  carbonates,  and 
know  that  they  correspond  to  a  carbonic  acid  which  should  con- 
lain  H2C03.     There  is  also  a  series  of  sulpho-carbonates,  exactly 
j-imilar  to  the  carbonates  in  composition,  but  they  contain  three 
sulphur  atoms  instead  of  three  atoms  of  oxygen. 

(H2C03),    Carbonic  acid.  H2CS3,      Sulphocarbonic  acid. 

Na2C03,    Sodium  carbonate.  Na.2CS3,    Sodium  sulpho-carbonate. 

K2C03,      Potassium  carbonate.       K2CS3,      Potassium  sulpho-carbonate. 

The  sulpho-carbonates  have  been  employed  to  destroy  low  forms 
of  life,  a  purpose  for  which  they  are  quite  effective. 

254.  If  we  compare  together  the  molecules  of  the  few  compounds  of  carbon 
Avhich  we  have  studied,  we  will  find  that  in  all  excepting  one  an  atom  of  car- 
bon has  as  much  combining  power  as  four  atoms  of  hydrogen.     It  is  tetra- 
tomic:  in  carbon  dioxide,  because  it  is  united  with  two  atoms  of  oxygen,  each 
of  which  is  worth  two  atoms  of  hydrogen  ;  in  sodium  carbonate,  for  it  is  there 
combined  with  one  atom  of  oxygen  and  two  other  atoms  of  oxygen,  each  of  which 
brings  into  the  system  a  sodium   atom  as  a  satellite;  in  carbon  disulphide, 


164 


LESSONS    IN    CHEMISTRY. 


where  it  is  combined  with  two  atoms  of  diatomic  sulphur;  and  there  is  also 
a  carbon  oxy  sulphide,  COS,  in  which  one  atom  of  oxygen  and  one  of  diatomic 
sulphur  satisfy  the  combining  capacity  of  the  tetratomic  carbon  atom.  How- 
ever, in  carbon  monoxide  either  the  carbon  atom  must  be  diatomic, — that  is, 
worth  two  atoms  of  hydrogen, — or  the  oxygen  atom  must  be  tetratomic.  Since 
we  know  that  carbon  monoxi  Je  can  combine  with  two  atoms  of  chlorine,  each 
of  which  has  the  power  of  one  hydrogen  atom,  and  that  it  may  also  combine 
with  another  oxygen  atom,  we  must  consider  that  the  carbon  atom  is  diatomic 
in  a  molecule  of  carbon  monoxide,  which  is  then  an  unsaturated  compound. 
We  may  represent  the  structure  of  these  molecules,  as  we  have  expressed  that 
of  others,  by  structural  formulae  : 


C=0  C1-C-C1 

0 

Carbon  Carbonyl 

monoxide.         chloride. 

After 


0=0=0 


Carbon 
dioxide. 


Sodium 
carbonate. 


NaO-C-ONa        S=C=S         0-C=S 
0 

Carbon          Carbon 
disulphide.  oxysulphide. 

time  we  shall  become  acquainted  with  compounds  in  which  the 
group  CS  acts  as  a  radical,  precisely  as  docs  the  group  carbonyl,  CO;  so  that 
we  may  consider  the  compound  COS  either  as  a  combination  of  carbonyl  with 
an  atom  of  sulphur,  or  as  a  compound  of  the  group  CS  with  one  atom  of 
oxygen  (g  278). 

255.  In  the  combining  power  of  its  atoms,  silicon  resembles  carbon.  It  also 
is  tetratomic,  as  we  can  understand  from  the  composition  of  the  silicon  com- 
pounds which  we  have  studied;  but  there  is  no  monoxide  corresponding  to 
carbon  monoxide,  and  silicon  does  not  appear  to  be  diatomic  in  any  com- 
pounds. 

0=SUO  HO-Si-OH  Fl-Si-Fl 

II  /\ 

0  F1-F1 

Silicic  oxide.  Silicic  hydrate.  Silicon  fluoride. 

256.  Cyanogen,  C2N2. — We  put  into  a  test-tube  some  mer- 
curic cyanide,  a  white  and 
very  poisonous  compound  of 
mercury,  carbon,  and  nitrogen; 
then  we  adapt  to  our  test-tube 
a  cork  in  which  we  have  fitted 
a  bent  tube  bearing  a  little 
bulb  containing  some  small 
pieces  of  the  metal  potassium 
(Fig.  81);  the  outer  end  of 
this  tube  is  drawn  into  a  fine 
jet.  We  now  heat  the  mer- 
curic cyanide,  and  presently  metallic  mercury  begins  to  deposit  in 


CYANOGEN.  165 

the  cooler  part  of  the  tube,  and  a  gas  is  escaping  from  the  jet : 
we  light  it,  and  it  burns  with  a  beautiful  peach-blossom-colorcd 
fl  ame. 

This  gas  is  cyanogen.  It  is  a  colorless  gas,  having  an  odor 
like  that  of  bitter  almonds,  and  is  quite  poisonous.  Its  density 
c  )m pared  to  air  is  1.8064,  or  compared  to  hydrogen,  26;  its 
iiolecular  weight  is,  then,  52,  and  analysis  has  shown  that  it  con- 
t  dns  carbon  and  nitrogen  in  the  proportions  indicated  for  one 
u:om  of  each.  Since  its  molecular  weight  is  52,  a  molecule  of 
cyanogen  gas  must  contain  two  atoms  of  carbon  and  two  of  nitro- 
Ljn.  Cyanogen  is  converted  into  a  liquid  by  pressure  or  by  a 
t  ;mperature  of  — 25°.  It  dissolves  in  about  one-quarter  its 
\  ;>lume  of  water,  but  the  solution  soon  decomposes,  and  then 
u  ways  contains  ammonia  or  some  ammonium  compound.  The 
c  )rnbustion  of  cyanogen  produces  nitrogen  and  carbon  dioxide. 

257.  By  the  aid  of  a  spirit-lamp,  we  now  heat  the  bulb  con- 
t  lining  the  potassium.  There  is  a  bright  flash  of  light :  the 
j  Dtassium  and  cyanogen  have  combined,  and  formed  potassium 
c  ;anide.  Cyanogen  is,  then,  capable  of  entering  into  combination. 
When,  however,  we  analyze  the  potassium  cyanide  formed,  we 
find  that  it  contains  potassium,  carbon,  and  nitrogen  in  the  pro- 
p  >rtions  required  for  one  atom  of  each  ;  its  formula  is  KCN. 
The  cyanogen  molecule  C2N2  has  then  separated  into  two  groups 
CN,  each  of  which  has  combined  with  an  atom  of  potassium. 
Ilie  group  CN  is  a  radical,  and  free  cyanogen  resembles  free  chlo- 
rine in  this  respect,  for  the  molecule  of  chlorine  contains  two 
atoms,  while  the  molecule  of  cyanogen  contains  two  groups  or 
radicals. 

Cl-Cl  NC-CN 

The  reaction  between  potassium  and  cyanogen  is,  then,  like  that 
between  potassium  and  chlorine;  both  are  double  decompositions. 

K-K  +  Cl-Cl  =  KCl     +  KC1 

K-K   +  (CN)-(CN)  =  KCN  +  KCN 

258.  In  free  cyanogen  gas  is  it  the  carbon  atoms  which  are  united  together, 
or  the  nitrogen  atoms?  When  cyanogen  or  its  compounds  decompose,  the  ni- 
trogen atoms  always  form  compounds  in  which  they  are  triatomic,  having  the 
combining  power  of  three  atoms  of  hydrogen.  Then  we  must  believe  that  they 


166  LESSONS    IN    CHEMISTRY. 

are  also  triatomic  in  cyanogen,  and  since  the  carbon  atom  is  worth  four  hydro- 
gen atoms  and  the  nitrogen  atom  only  satisfies  three-fourths  of  this  combining 
power,  the  carbon  atoms  must  be  united  together,  and  we  consequently  write 
cyanogen  gas  NEC-CEN  or  (CN)2.  We  see  also  that  the  potassium  atom  in 
potassium  cyanide,  and  the  mercury  atom  in  mercuric  cyanide,  must  be  united 
to  the  carbon  atom  of  cyanogen.  (Compare  $$  262  and  334.) 

K-CIN  NlC-Hg-CEN 

Although  carbon  and  nitrogen  do  not  combine  directly,  potassium  cyanide 
is  formed  when  either  nitrogen  gas  or  ammonia  is  passed  over  a  highly  -heated 
mixture  of  charcoal  with  potassium  carbonate  or  potassium  hydrate.  All  of 
the  compounds  of  cyanogen  are  prepared  from  potassium  ferrocyanide  (§  266). 


LESSON    XXXII. 
HYDROCYANIC   ACID.— CYANIDES. 

259.  Hydrocyanic  Acid,  HON. — This  dangerous  poison,  com- 
monly called  prussio  acid,  is  formed  when  a  cyanide  is  treated 
with  a  dilute  acid ;  as  by  the  action  of  hydrochloric  acid  on  mer- 
curic cyanide. 

Hg(CN)2         +         2HC1         *=         HgCl2         +         2HCN 
Mercuric  cyanide.  Mercuric  chloride. 

It  is  usually  made  by  distilling  8  parts  of  potassium  ferrocya- 
nide with  a  cooled  mixture  of  9  parts  of  sulphuric  acid  and  14 
parts  of  water.  The  beak  of  the  retort  containing  this  mixture  is 

inclined  upwards,  in  order 
that  the  water  may  condense 
and  run  back  into  the  retort ; 
the  vapor  of  hydrocyanic  acid 
is  dried  by  passing  through  a 
calcium  chloride  tube  placed 
in  water  heated  to  about  30°, 
and  then  condensed  in  a  flask 
surrounded  by  a  mixture  of  ice  and  salt  (Fig.  82). 

260.  Hydrocyanic  acid  is  a  colorless,  very  volatile  liquid  ;  its 
odor  resembles  that  of  bitter  almonds.     Its  density  is  about  0.7  ; 


HYDROCYANIC    ACID.  167 

it  freezes  at  — 15°,  and  boils  at  26.5°.  The  density  of  its  vapor 
compared  to  hydrogen  is  13.5,  corresponding  exactly  with  the 
molecular  weight  implied  by  the  formula  HCN.  It  dissolves  in 
all  proportions  of  water,  and  a  two  per  cent,  solution  is  used  in 
m<  dicine.  It  is  combustible,  and  when  ignited  burns  into  water, 
ca  bon  dioxide,  and  nitrogen.  It  is  exceedingly  poisonous,  and 
th  *,  accidental  inhalation  of  its  vapor  has  in  some  cases  proved 
fatal. 

261.  It  is  often  important  to  be  able  to  recognize  hydrocyanic 
ac.dj  and  we  may  do  so  by  the  following  tests.  We  make  our 
so  ution  of  hydrocyanic  acid  for  these  tests  by  adding  a  little  dilute 
su  phuric  acid  to  some  solution  of  potassium  cyanide.  The  liquid 
th  :n  contains  hydrocyanic  acid  and  potassium  sulphate. 

Over  the  beaker  glass  in  which  we  have  prepared  this  solution, 
Wt   invert  a  watch-glass  or  glass  plate  on  which  we 
hi  ve  placed  a  drop  of  silver  nitrate  solution  (Fig. 
8i  ) :  this  drop  soon  becomes  clouded  from  the  for- 
m  tion  of  insoluble  silver  cyanide ;  the  white  de- 
pi  sit  does  not  darken  quickly  on  exposure  to  light, 
an  1  is  dissolved  by  nitric  acid ;  these  characters  dis- 
tii  guish   it  from    silver  chloride,   which   would  be       yIG  §3 
foimed  if  the  liquid  contained  hydrochloric  acid. 

We  now  invert  over  our  beaker  another  watch-glass  containing 
a  drop  of  ammonium  sulphide  which  has  become  yellow  by  expo- 
su -e  to  light  and  air:  some  ammonia  has  escaped  from  it,  and  it 
contains  an  excess  of  sulphur.  In  a  little  while  this  drop  becomes 
colorless :  a  compound  called  ammonium  sulphocyanate  has  been 
formed  in  it. 


+     S2     +_    2HCN     .  =     2NH4CSN     +     H2S 
Ammonium  Ammonium 

sulphide.  sulphocyanate. 

If  we  now  carefully  warm  the  spot  until  it  no  longer  has  the  odor 
of  hydrogen  sulphide,  and  th?n  touch  it  with  a  drop  of  ferric 
chloride  solution,  a  blood- red  color  appears.  This  color  is  due  to 
the,  formation  of  ferric  sulphocyanate  (§  277). 

We  mix  in  a  test-tube  a  few  drops  of  our  hydrocyanic  acid 


168  LESSONS    IN   CHEMISTRY. 

solution  with  a  little  ferrous  sulphate  and  ferric  sulphate,  and  add 
a  little  strong  solution  of  sodium  hydrate :  a  dirty  deposit  forms, 
but  when  we  add  an  excess  of  hydrochloric  acid,  a  part  of  the 
deposit  is  dissolved,  and  a  fine  blue  precipitate,  Prussian  blue 
(§  267),  remains. 

262.  Hydrocyanic  acid  does  not  keep  long,  soon  decomposing,  whether  it  be 
pure  or  in  solution.  It  undergoes  an  interesting  reaction  with  strong  hydro- 
chloric acid,  and  the  reaction  is  more  interesting  because  it  is  characteristic 
of  all  the  cyanides.  When  we  mix  hydrocyanic  acid  with  strong  hydro- 
chloric acid,  the  mixture  becomes  hot,  and  a  mass  of  crystals  of  ammonium 
chloride  separate.  The  most  curious  part  of  this  reaction  is,  that  it  takes 
place  between  the  hydrocyanic  acid  and  the  water  of  the  hydrochloric  acid ; 
the  nitrogen  atom  of  the  former  is  exchanged  for  an  atom  of  oxygen  and  a 
hydroxyl  group. 

HCN     +     2H2Q     =     HCO.OH     +     NR3 

The  ammonia  formed  combines  with  the  hydrochloric  acid.  The  compound 
HCO.OH  is  called  formic  acid.  When  a  solution  of  potassium  cyanide  is 
boiled,  it  is  converted  into  potassium  formate  by  a  similar  reaction. 

KCN         +         2H20        =        HCO.OK         +        NH» 
Potassium  cyanide.  Potassium  formate. 

All  the  acids  of  carbon  which  we  shall  presently  have  occasion  to  study, 
may  be  formed  by  the  replacement  of  the  nitrogen  atoms  of  corresponding 
cyanides  by  an  oxygen  atom  and  a  hydroxyl  group. 

263.  Potassium  Cyanide,  KCN,  is  made  by  heating  dry  po- 
tassium ferrocyanide  red  hot  in  earthen  retorts.     After  the  mass 
cools,  it  is  extracted  with  alcohol,  and  when  the  filtered  liquid  is 
evaporated  it  leaves  a  white  mass  of  potassium  cyanide.     It  may 
be  crystallized  in  cubes.     It  is  soluble  in  water  and  alcohol,  but 
the  aqueous  solution   decomposes  after  a  time,  even  in  the  cold, 
into  potassium  formate  and  ammonia.      When  potassium  cyanide 
is  heated  with  sulphur,  it  is   converted   into  potassium  sulpho- 
cyanate,  CSNK.     Solutions  of  potassium  cyanide  dissolve  the  in- 
soluble cyanides  of  silver,  zinc,  and  other  metals,  forming  double 
cyanides,  which  are  used  in  electro-plating.     Potassium  cyanide  is 
very  poisonous,  as  indeed  are  nearly  all  the  cyanides. 

264.  Silver  Cyanide,  AgCN,  is  formed  as  a  white  precipitate 
when  a  solution  of  silver  nitrate  is  treated  with  the  exact  quantity 
of  potassium  cyanide  required  for  one  molecule  of  each.     When 
heated,  it  decomposes  into  silver  and  cyanogen  gas. 


CYANIDES.  169 

265.  Mercuric  Cyanide,  Hg(CN)2.— -This  compound  may  be 
made  by  dissolving  mercuric  oxide  in  dilute  hydrocyanic  acid,  but 
ii  is  usually  prepared  by  boiling  for  about  fifteen  minutes  a  mix- 
ture of  one  part  of  potassium  ferrocyanide,  two  parts  of  mercuric 
tvilphate,  and  eight  parts  of  water.     The  mixture  is  filtered  while 
I  oiling,  and  mercuric  cyanide  separates  from  the  filtrate  in  color- 
I'-ss,  anhydrous,  square  prisms,     It  dissolves  in  eight  times  its 
v  eight  of  cold  water. 

266.  Potassium  Ferrocyanidet  K4Fe(CN)6.— Potassium  fer- 
i  ^cyanide  is  the  starting-point  for  the  preparation  of  other  com- 
}  juuds  of  cyanogen.     There  are  a  number  of  processes  for  its 
Manufacture :  the  most  common  of  them  consists  in  heating  waste 
ci  limal  matters  containing  nitrogen,  such  as  blood,  horn,  scraps  of 
fc-  dn  and  leather,  with  potassium  carbonate  and  scrap  iron.     After 
t  le  mass  has  cooled,  it  is  exhausted  with  boiling  water,  and  the 
c  jncentrated  solution  deposits  the  ferrocyanide  in  crystals. 

These  crystals  are  yellow,  and  contain  three  molecules  of  water 
of  crystallization,  which  may  be  driven  out  by  a  temperature  of 
1 00°  ;  the  anhydrous  salt  then  remains  as  a  white  powder.  Crys- 
t  illine  potassium  ferrocyanide,  which  is  commonly  called  yellow 
1  russiate  of  potash,  dissolves  in  four  times  its  weight  of  cold  or 
rvice  its  weight  of  boiling  water,  and  is  insoluble  in  alcohol.  It 
i>  not  poisonous. 

The  group  of  atoms  Fe(CN)6  which  it  contains  is  a  radical,  and 
t;  kes  part  in  double  decompositions  without  undergoing  change. 
There  is  a  hydroferrocyanic  acid,  H4Fe(CN)6.  We  add  some 
cupric  sulphate  to  solution  of  potassium  ferrocyanide,  and  a  ma- 
hogany-colored precipitate  of  cupric  ferrocyanide  is  formed,  while 
potassium  sulphate  goes  into  solution. 

2CuSO*     +     K4Fe(CN)6     =  =     2K2SO*     +     Cu2Fe(CN)6 

Solution  of  potassium  ferrocyanide  causes  the  formation  of 
insoluble  fcrrocyanides  in  solutions  of  many  metallic  salts,  and 
tlie  color  of  the  precipitate  is  a  means  frequently  employed  for 
identifying  the  metals.  With  zinc  sulphate,  we  would  have  zinc 
ferrocyanide,  which  is  white,  thrown  down. 
H  15 


170  LESSONS   IN   CHEMISTRY. 

When  potassium  ferrocyanide  is  heated  to  redness  in  closed  vessels,  it  is 
converted  into  potassium  cyanide,  while  iron  and  charcoal  separate  and  nitro- 
gen is  disengaged.  When  it  is  heated  in  the  air  or  with  certain  oxidizing 
agents,  it  yields  potassium  isocyanate,  CONK.  Under  the  same  circumstances 
with  sulphur  it  forms  potassium  sulphocyanate,  CSNK. 

267.  Prussian  Blue,  Ferric  Ferrocyanide,  (Fe2)2(FeC6N6)3. 
— When  ferrous  sulphate,  FeSO4,  is  added  to  a  solution  of  potas- 
sium ferrocyanide,  the  atom  of  iron  changes  place  with  two  atoms 
of  potassium,  and  a  pale-blue  precipitate  containing  FeK2Fe(CN)6 
is  formed.     When,  however,  potassium  ferrocyanide  is  added  to  a 
ferric  salt,  such  as  ferric  chloride,  Fe2Cl6,  a  dark-blue  precipitate 
of  Prussian  blue  is  thrown  down.     As  the  two  atoms  of  iron  in 
ferric  chloride  replace  six  atoms  of  hydrogen  in  as  many  molecules 
of  hydrochloric  acid,  they  will  also  replace  six  atoms  of  potassium, 
and  we  must  write 

2Fe2Cl6         +  3K4Fe(CN)&  =         12KC1     +     Fe4(FeC6N6)3 

Ferric  chloride.          Potassium  ferrocyanide.  Prussian  blue. 

Prussian  blue,  much  used  as  a  pigment,  generally  comes  in 
cubical  masses  having  a  coppery  reflection.  It  is  insoluble  in 
water,  and  in  dilute  acids,  with  the  exception  of  solutions  of  oxalic 
acid.  It  is  dissolved  by  alkaline  hydrates,  which  destroy  its  color. 

While  we  are  uncertain  of  the  exact  relations  cf  the  atoms  in  the  mole- 
cules of  the  ferrocyanides,  yet  we  have  learned  that  they  contain  a  distinct 
radical,  ferrocyanogen,  Fe(CN)6;  and  we  see  that  the  relations  of  the  atom  of 
iron  in  this  radical  are  quite  different  from  those  of  the  four  iron  atoms  in 
Prussian  blue.  The  latter  readily  leave  and  re-enter  the  molecule  by  double 
decomposition,  but  the  iron  atom  in  ferrocyanogen  always  goes  with  the  six 
groups,  CN,  unless  the  molecule  be  decomposed  by  heat  or  energetic  chemical 
agents.  Indeed,  two  ferrocyanogen  groups  may  combine  together,  as  is  the 
case  in 

268.  Potassium  Ferricyanide,  K6(FeC6N6)2.   This  compound 
is  formed  by  passing  chlorine  gas  into  a  solution  of  potassium  fer- 
rocyanide.    One  atom  of  potassium  is  then  removed  from  each 
molecule  of  the  ferrocyanide,  forming  potassium  chloride,  and  the 
remainders  of  the  molecules  unite  together  in  pairs,  forming  potas- 
sium ferricyanide. 

2K*FeC6N6         +         Cl2        =         2KC1         +         K«(FeC«N«j2 
Potassium  ferrocyanide.  Potassium  ferricyanide. 


POTASSIUM    ISOCYANATE.  171 

Potassium  ferricyanide  forms  beautiful,  large,  ruby-red,  anhy- 
dious  crystals.  It  dissolves  in  about  four  times  its  weight  of  cold 
w  iter,  and  the  solution  has  a  greenish-brown  color.  It  forms  no 
precipitate  with  ferric  salts,  but  with  ferrous  sulphate  gives  a  dark- 
blae  precipitate  of  ferrous  ferricyanide,  called  Turnbull's  blue. 

K6(FcC«N6)2          +          SFeSO*  -      SK'SO*     +     Fe3(FeC6N<5)2 

P  tassiuiu  ferricyaiiide.        Ferrous  sulphate.  Turnbull's  blue. 


LESSON    XXXIII. 

CARBONYL   COMPOUNDS. 

269.  We  have  already  seen  that  carbon   monoxide  combines 
d  rectly  with  chlorine,  forming  carbonyl  chloride,  COCP.     To  this 
cl  loride  there  corresponds  a  series  of  compounds   in  which  the 
c)  lorine  atoms  are  replaced  by  various  radicals  having  the  same 
ci  mbining  power.     The  only  compounds  of  this  class  which  we 
c;  n  consider  are  the  isocyanates,  urea,  and  a  few  closely-allied 
si.bstances. 

270.  Potassium    Isocyanate,    CO.NK. — When   an   intimate 
m  xture   of  perfectly  dry  potassium   ferrocyanide  with    half  its 
weight  of  manganese  dioxide  is  heated  to  dull  redness  with  con- 
st;.nt  stirring,  the  mixture  becomes  black  and  pasty.     The  potas- 
sium ferrocyanide  has  been  decomposed,  and  potassium  isocyanate 
exists  in  the  product.     To  extract  this  substance,  the  black  mass 
is  finely  powdered  and  the  powder  shaken  up  with  boiling  eighty 
per  cent,  alcohol:  the  liquid  is  quickly  decanted  from  the  sedi- 
ment, and  on  cooling  deposits  potassium  isocyanate  in  small,  color- 
less, anhydrous  crystals.    It  is  very  soluble  in  water;  only  slightly 
soluble  in  cold  alcohol.     When  the  aqueous  solution  is  heated,  the 
isocyanate  is  decomposed  into  potassium  carbonate,  carbon  dioxide, 
and  ammonia. 

2CO.NK         +         3H2Q         =         KXIO3         +         CO2         +         2NH3 
Potassium  isocyanate  is   decomposed  in  the  same  manner  by 
acids  :  hydrochloric  acid  converts  it  into  potassium  chloride  and 


172  LESSONS    IN    CHEMISTRY. 

ammonium  chloride,  while  carbon  dioxide  escapes  with  efferves- 
cence. " 

CO.NK     +     2HC1     +     H2Q     =     KC1     +     NH*C1     +     CO2 

The  acid  corresponding  to  potassium  isocyanate  is  of  course 
isocyanic  acid,  CO.NH,  but  it  cannot  be  made  by  double  decom- 
position with  potassium  isocyanate. 

271.  There  is  another  compound  whose  molecule  has  exactly 
the  same  composition  as  that  of  potassium  isocyanate,  and  the  cor- 
responding acid,  although  not  yet  separated,  is  cyanic  acid.     It 
would  contain  the  radical  cyanogen,  ON,  and  a  hydroxyl  group, 
OH ;  the  potassium  salt  representing  this  molecule,  in  which  the 
hydrogen   atom  is  replaced   by  potassium,  contains  K-0-C=N. 
It  has  been  obtained  by  the  action  of  a  compound  called  cyano- 
gen chloride,  C1-C~N,  on  potassium  hydrate. 

Cl-CzN  +  2KOH  =  KC1  +  H2Q  +  KO-CZN 
This  is  the  true  potassium  cyanate  ;  the  other  compound  has 
precisely  the  same  atoms  in  its  molecule,  but  we  shall  presently 
find  reasons  for  believing  that  these  atoms  are  differently  arranged. 
Compounds  whose  molecules  contain  the  same  number  and  kind 
of  atoms,  and  yet  have  different  properties,  are  called  isomeric 
compounds.  There  are  two  isomeric  potassium  compounds  whose 
molecules  contain  one  atom  each  of  potassium,  carbon,  oxygen,  and 
nitrogen  :  that  containing  the  radical  cyanogen  is  called  potassium 
cyanite ;  the  other,  which  we  shall  see  does  not  contain  that  radical, 
is  called  potassium  isocyanate.  The  relations  of  the  atoms  in  its 
molecule  are  expressed  by  the  formula  O^C^NK  (§  274). 

272.  Ammonium   Isocyanate,   NH*.NCO,   is  formed   when 
vapor  of  isocyanic   acid  is  mixed  with   ammonia  gas.  .    It  is  a 
white  solid,  very  soluble  in  water.     When  its  aqueous  solution  is 
boiled,  or  even  left  to  itself  for  a  few  days,  the  ammonium  iso- 
cyanate is  converted  into  an  isomeric  body,  urea. 

273.  Urea,   CO(NH2)2,  may  be  formed  by  a  reaction  which 
establishes  its  molecular  structure  beyond  doubt.     When  carbonyl 
chloride,  COC12,  is  made  to  react  with  ammonia,  urea  and  hydro- 
chloric acid  are  formed. 

COOP         +         2NH3        =         CO(NH2)2         +         2HC1 
Carbonyl  chloride.  Urea. 


AMMONIUM    ISOCYANATE.  173 

Here  two  molecules  of  ammonia  lose  each  one  atom  of  hydro- 
gen, which  combines  with  the  chlorine  of  the  carbonyl  ch'loride, 
and  the  unsatisfied  groups  CO  and  2NH2  combine,  forming  a 
molecule  of  urea.  The  group  NH2  passes  readily  from  one  mole- 
cule to  another  by  double  decomposition.  It  represents  a  molecule 
of  ammonia  from  which  an  atom  of  hydrogen  has  been  removed : 
it  is  a  monatomic  radical.'  We  may  then  consider  that  urea  is 
fo  med  from  two  molecules  of  ammonia  by  the  replacement  of 
01  3  atom  of  hydrogen  of  each  by  the  diatomic  radical  carbonyl. 
C«  mpounds  formed  by  the  replacement  of  the  hydrogen  atoms  of 
an  monia  by  other  atoms  or  groups  are  called  amines  or  amides  : 
wl  en  the  replacement  is  by  the  radicals  of  acids,  the  name  amide 
is  ased  to  designate  the  new  compound,  while  amine  is  applied  to 
su  :h  compounds  as  result  from  the  replacement  of  these  hydrogen 
at  'ins  by  radicals  which  are  also  capable  of  replacing  the  hydrogen 
oi  acids.  Since  carbonyl  is  the  radical  of  carbonic  acid,  which 
is  carbonyl  dihydrate,  CO(OH)2,  we  call  urea  carbonyl  amide,  or 
ca  'bamide. 

274.  We  have  already  learned  that  urea  is  formed  by  a  curious 
cli  mge  which  takes  place  in  ammonium  isocyanate.  Since  we 
can  readily  prepare  potassium  isocyanate,  we  have  a  ready  means 
of  obtaining  urea.  For  this  purpose  potassium  isocyanate  is 
pr<  pared  as  has  already  been  described  (§  270) ;  but,  instea^  of 
exhausting  the  mass  with  alcohol,  we  exhaust  it  with  cold  water, 
which  dissolves  out  the  isocyanate.  The  solution  is  then  mixed 
with  ammonium  sulphate  in  quantity  equal  to  five-sevenths  of 
tht  potassium  ferrocyanide  used,  and  the  whole  is  evaporated  to 
dryness  on  a  water-bath.  The  ammonium  sulphate  reacts  with 
the  potassium  isocyanate,  forming  potassium  sulphate  and  ammo- 
nium isocyanate,  and  the  latter  becomes  converted  into  the  isomeric 
compound,  urea.  The  mixture  of  the  two  bodies  is  extracted  with 
a  small  quantity  of  boiling  alcohol,  which  does  not  dissolve  the 
potassium  sulphate,  but  dissolves  the  urea,  and  on  cooling  deposits 
it  in  crystals. 

Since  there  can  be  no  question  that  urea  contains  the  group  carbonyl,  CO, 
united  to  two  groups  NH2, — in  chemical  language,  that  it  is  carbonyl  amide. 

15* 


174  LESSONS   IN    CHEMISTRY. 

or  carbamide, — we  must  infer  that  ammonium  isocyanate,  and  the  potassium 
isocyanate  from  which  it  is  derived,  also  contain  the  group  carbonyl. 

H4N-N=CO  CO(NH«)2 

Ammonium  isocyanate.  Urea. 

275.  Urea  is  the  principal  solid  constituent  of  the  urine :   it 
is  in  this  compound  that  the  greater  part  of  the   nitrogen  of 
burned  tissues  is  removed  from  the  body.     It  may  be  extracted 
from  urine  by  evaporating  the  liquid  to  a  thick  syrup,  and  adding 
nitric  acid  when  it  has  cooled.     The  nitric  acid  combines  with 
the  urea,  forming  urea  nitrate,  CO(NH2)2.HN03,  which  separates 
in  a  mass  of  crystals.     These  are  drained,  and  treated  with  a  con- 
centrated solution  of  potassium  carbonate  as  long  as  there  is  effer- 
vescence.    The  mixture  is  then  evaporated  to  dryness,  and  the 
urea  is  dissolved  from  the  potassium  nitrate  by  boiling  alcohol. 

276.  Urea  forms  colorless  crystals  having  a  cooling  taste.     It 
dissolves  in  its  own  weight  of  water,  and  in  five  times  its  weight 
of  cold  alcohol ;  it  is  very  soluble  in  boiling  alcohol.     An  aqueous 
solution  of  chlorine  instantly  decomposes  it,  setting  free  nitrogen 
and  carbon  dioxide. 

CO(NH2)2     +     H20     +     3C12    =     CO2     +     N2     +     6HCI 

By  the  action  of  heat,  its  solution  in  water  is  converted  into 
ammonium  carbonate. 

CO(NH2)2     +     2H20     =     (NH*)2C03 

Tj^e  same  reaction  takes  place  slowly  in  urine,  and  accounts  for 
the  ammoniacal  odor  of  stale  urine. 

277.  Potassium    Sulphocyanate,    KN.CS. — A    mixture    of 
potassium  ferrocyanide  with  half  its  weight  of  flowers  of  sulphur 
is  heated  to  dull  redness  in  a  covered  crucible.     After  cooling,  the 
mass  is  dissolved  in  water,  the   liquid  is  filtered,  and  potassium 
carbonate  is  added  as  long  as  it  causes  any  precipitate.     Then  the 
liquid  is  again  filtered,  and  the  solution  evaporated  to  dryness. 
The  residue  is  extracted  with  hot  alcohol,  and  the  alcoholic  solu- 
tion allowed  to  evaporate.     Potassium  sulphocyanate  then  sepa- 
rates in  colorless,  deliquescent  crystals  which  are  very  soluble  in 
water  and   in   alcohol.     A   solution  of  potassium   sulphocyanate 
produces  a  blood-red  color  (ferric  sulphocyanate)  with  solutions 
containing  ferric  salts. 


METHANE.  175 

Potassium  sulphocyanate  corresponds  to  the  isocyanate  in  vvhicli 
the  oxygen  atom  is  replaced  by  an  atom  of  sulphur. 

278.  Ammonium  Sulphocyanate,  (NH4)N.CS,  is  found  in  small  quantity 
ii  the  water  which  has  been  used  to  wash  coal  gas  ($  225).  Representing  am- 
n  onium  isocyanate  in  which  the  oxygen  is  replaced  by  sulphur,  it  undergoes 
!>>•  the  action  of  heat  a  similar  curious  change  into  the  isomeric  compound 
.-•  'Ipho-urea,  CS(NH2)2,  whose  molecule  is  exactly  like  that  of  urea,  excepting 
t  i at  it  contains  sulphur  instead  of  oxygen.  It  contains  the  radical  CS  (g  254). 


LESSON    XXXIV. 
COMPOUNDS    OF   CARBON  AND   HYDROGEN  (i). 

279.  Methane,  CH4. — In  a  glass  flask  on  a  sand-bath  we  heat 
mixture  of  equal  parts  of  dried  sodium  acetate,  sodium  hydrate, 
nd  powdered  lime  (Fig.  84).  The  lime  does  not  enter  into  the 


FIG.  84. 

reaction  which  takes  place,  but  it  prevents  the  hot  sodium  hydrate 
from  melting  through  the  glass.  Since  gas  will  be  disengaged, 
we  have  adapted  to  our  flask  a  cork  and  tube,  and  may  collect  this 
gas  over  water,  in  which  it  is  almost  insoluble.  The  gas  is  methane : 
k  is  produced  by  a  reaction  between  the  sodium  acetate  and  sodium 
hydrate,  which  at  the  same  time  yield  sodium  carbonate. 

NaC2IW         +         NaOH  NaZOO3  +         C1I4 

Sodium  acetate.  Sodium  carbonate.  Methane. 


176  LESSONS    IN    CHEMISTRY. 

280.  It  is  a  colorless  gas,  having  no  odor.  Its  density  compared 
to  air  is  0.559,  or  compared  to  hydrogen,  8 :  this  corresponds  to  a 
molecular  weight  of  16,  as  is  indicated  by  the  formula,  CH4.  It 
is  a  combustible  gas,  and  burns  with  a  yellow  flame.  It  forms  an 
explosive  mixture  with  air  or  oxygen,  and  this  mixture  is  often 
unfortunately  formed  in  the  galleries  of  coal-mines,  for  methane  is 
the  fire-damp  of  the  miners.  It  exists  under  strong  pressure  in 
the  coal-beds,  and  escapes  when  these  beds  are  cut  into  by  the 
miners. 

We  have  already  learned  that  a  certain  temperature  is  necessary 
for  combustion,  as  indeed  for  all  chemical  action,  and  a  gas  cannot 
continue  burning  when  its  flame  is  cooled  below  the  igniting  point. 
When  a  flame  is  inserted  in  a  tube,  not  too  wide,  it  is  extinguished, 
because  the  walls  of  the  tube  cool  it.  For  this  reason  the  flame 
does  not  run  down  the  tube  of  a  good  Bunsen  burner,  although 
the  combustible  gas  is  mixed  with  air.  A  piece  of  wire  gauze 
may  be  regarded  as  composed  of  a  large  number  of  fine,  short 
tubes,  and  wire  gauze  will  prevent  the  passage  of  flame.  The 
fineness  of  the  gauze  required  will  depend  on  the  igniting  point 
of  the  gas  or  vapor,  and,  as  this  temperature  is  lower,  the  gauze 
must  be  finer.  We  may  depress  a  piece  of  wire  gauze  in  the  flame 
of  a  Bunsen  burner  or  a  lamp,  and  the  flame  is  kept  below  the 
gauze  until  the  latter  is  heated  to  the  temperature  required  for 

the  combustion  of  the  gas. 
Yet  the  combustible  gas 
passes  through,  and  we  may 
light  it  above  the  gauze :  in 
the  same  manner  we  may 
hold  the  gauze  a  short  dis- 
tance above  the  burner  in 
the  escaping  but  unlighted 
FIG.  85.  gas,  and  we  may  ignite  the 

gas  above  the  gauze ;   the 

flame  does  not,  however,  pass  below  until  the  gauze  becomes 
heated  as  before  (Fig.  85).  These  principles  are  applied  in  the 
miners7  safety-lamp,  which  is  practically  a  lamp  so  arranged  that  air 


METHANE. 


177 


can  pass  to  the  flame  and  the  burned  gases  escape  only  through 

tin-  meshes  of  fine  wire  gauze  (Fig.  86).     For 

better  illumination,  that  part  of  the  gauze  im- 
mediately around  the  flame  is  usually  replaced 

by  thick  glass.    The  explosive  gases  may  enter 

th's  lamp,  and  may  burn  inside,  but  the  flame 

ca  mot  pass  through  unless  the  gauze  become 

hi  rhly  heated.     In  most  countries  it  is  unlaw- 

fu    to   continue  working   galleries  containing 

ex  plosive  gases  until  those  gases  are  removed 

b\    ventilation.       The    safety-lamp    affords    a 

rn  aus  of  detecting  the  presence  of  very  small 

qv  an  titles  of  such   gases  without   danger  of 

exploding  them.      We  pass  a  very  little  illu- 

in  nating  gas  or  some  of  our  methane  into  an 

in  'erted  jar,  and  thoroughly  mix  it  with  the 

ai    in  the  jar  by  moving  a  roll  of  paper  around 

in  it.     We  now  push  up  into  the  jar  a  lighted 

w;  x  taper,  the  end  of  which  projects  just  be- 

yi  nd  a  small  glass  tube  slipped  over  it,  so  that 

th  3  flame  is  quite  small.    WTe  see  that  this  small 

flame  is  surmounted  by  a  pale  and  tremulous 

bliish  cap  (Fig.   87):   this  is   owing  to  the 

coubustion  of  the  mixture  of  gas  and  air  im- 
mediately around  the  flame,  but  there  is  so 
litrle  of  the  combustible  gas  present  that  the 
heat  produced  by  its  combustion  immediately  around  the  flame  is 
not  sufficient  to  carry  the  combustion  throughout  the  whole  mix- 
ture; otherwise  there  would  be  an  explosion.  By  looking  at  the 
flame  in  his  safety-lamp,  the  miner  can  tell  by  the  presence  or 
absence  of  this  bluish  cap  whether  any  fire-damp  be  present,  and, 
if  so,  whether  there  be  sufficient  to  indicate  danger  of  explosion. 
281.  Methane  is  one  of  the  products  of  the  putrefaction  of 
vegetable  matters  in  presence  of  water.  It  is  formed  by  the  de- 
composition of  such  substances  in  the  muddy  bottoms  of  ponds 
and  rivers,  and  rises  in  bubbles  through  the  water  when  this  mud 


FIG.  86. 


178  LESSONS    IN   CHEMISTRY. 

is  stirred :  it  often  collects  under  the  ice  in  winter,  and  will  escape 
and  burn  with  a  pale  flame  when  the  ice  is  pierced  and  the  gas 
lighted.  Because  of  its  formation  in  these 
localities,  methane  is  often  called  marsh  gas. 

282.  The  composition  of  methane  shows  us  that  the 
carbon  atom  is  tetratornic ;  it  has  the  combining  power 
of  four  atoms  of  hydrogen.     We  have  already  learned 
that  chlorine  has  an   energetic  affinity  for  hydrogen, 
and  that  it  will  remove  this  element  from  many  hy- 
drogen   compounds.     When    chlorine    is    mixed   with 
methane,   and   the   mixture    is    exposed   to   light,   the 
chlorine  removes  the  hydrogen  from  the  methane,  and 
hydrochloric  acid  is  formed,  but  an  atom  of  chlorine 
takes  the  place  of  every  atom  of  hydrogen  so  removed. 
We  may  consider  that  there  is  a  double  decomposition 
FlG.  87.         *    between  the  chlorine  molecules  and  the  methane  mole- 
cules, and  this  decomposition  may  continue  until  all 
the  hydrogen  atoms  of  the  methane  are  replaced  by  chlorine. 
CH*     +     Cl2       =     CH3C1      +     HC1 
CH*     +     2C12     =     CH2C12    +     2HC1 
CH*     +     3C12     =»     CH.C13     +     3HC1 
CH*     +     4C12     =     CC14         +     4HC1 

All  these  compounds  of  carbon  with  chlorine  and  hydrogen  may  be  ob- 
tained in  this  manner.  Their  compositions  are  a  still  further  evidence  that 
the  carbon  atom  is  tetratomic.  The  hydrogen  atoms  of  methane  may  also  be 
replaced  by  the  monatomic  atoms  of  bromine  and  iodine,  producing  compounds 
precisely  similar  to  those  formed  by  chlorine. 

One  of  the  substances  so  formed  has  the  composition  CH3I;  it  is  called 
methyl  iodide,  and  the  compound  CH3C1  is  called  methyl  chloride.  We  may 
consider  that  the  group  of  atoms  CH3  acts  like  a  single  atom  of  potassium  in 
potassium  chloride  ;  and  when  we  have  learned  that  it  may  take  part  in  double 
decompositions,  leaving  one  molecule  and  entering  another  without  change, 
we  shall  see  that  it  is  a  radical;  it  is  called  methyl. 

283.  Methyl  iodide,  CH3I,  is  a  colorless  liquid.  When  it  is 
sealed  up  in  strong  glass  tubes  containing  some  zinc,  and  the 
tubes  are  heated  for  a  time  to  about  150°,  the  zinc  takes  away 
the  iodine  from  the  methyl  iodide,  and  zinc  iodide,  Znl2,  is 
formed.  When  the  tubes  are  carefully  opened,  they  are  found  to 
contain  a  gas  to  which  both  analysis  and  density  assign  the  com- 
position C2H6.  How  must  the  atoms  be  related  in  a  molecule  of 
this  gas  ?  Are  the  carbon  atoms  still  tetratomic  ?  How  has  the 


COMPOSITION    OF    HYDROCARBONS.  179 

<ya :•;  been  formed  ?     We  must  believe  that   when   two  atoms  of 

O 

iotiine  are  removed  from  two  molecules  of  methyl  iodide  the  two 
mcnatomic  methyl  groups,  CH3,  combine  together;  that  in  a  mol- 
ecule of  the  gas,  C2H6,  the  two  carbon  atoms,  each  with  its  three 
hydrogen  atoms,  like  three  satellites,  form  a  perfect  system.  We 
ca  i  represent  this  relation  by  our  formulas. 

CH3I  +  Zn         +  ICH3  ZnP        +       H3C-CH3 

Me  i hyl  iodide.  Zinc.  Methyl  iodide.      Zinc  iodide.  Ethane. 

Then  in  this  gas,  L2H6,  which  is  called  ethane,  the  affinity  of 
tit  a  carbon  atoms  must  be  satisfied  partly  by  their  combination 
to  Aether,  and  partly  by  their  combination  with  hydrogen. 

284.  By  the  action  of  chlorine  on  ethane,  the  hydrogen  of  that 
g:  s  may  be  replaced  by  chlorine  atoms,  and  compounds  may  also 
bi  obtained  in  which  the  replacement  is  by  iodine  atoms.  When 
01  ly  one  of  the  hydrogen  atoms  is  so  replaced,  the  compound 
C  H5I  is  formed.  We  consider  that  this  contains  the  radical 
C  H5,  which  is  called  ethyl,  and  the  molecule  C2H5I  is  called 
ct  tyl  iodide.  Since  all  the  atoms  of  hydrogen  in  a  molecule  of 
et  lane  must  have  the  same  relations  to  the  carbon  atom  around 
w  lich  they  move,  and  also  to  the  other  carbon  atom,  it  is  a  matter 
of  indifference  which  one  we  suppose  to  be  replaced  by  the  iodine 
at  >m.  When  ethyl  iodide  and  methyl  iodide,  in  the  proportions 
required  for  the  same  number  of  molecules  of  each,  are  heated 
with  zinc  in  sealed  tubes,  a  reaction  takes  place  just  as  in  the  case 
of  zinc  and  methyl  iodide  alone.  That  is,  both  iodine  atoms  are 
re  noved,  and  we  may  say  either  that  the  iodine  of  ethyl  iodide 
is  replaced  by  the  group  methyl,  CH3,  or  that  the  iodine  of  methyl 
iodide  is  replaced  by  the  radical  ethyl,  C2H5.  A  gas  called  pro- 
pane, C3H8,  is  then  formed. 

C2H5I         +         Zn     +     1C  II3         =        ZnP        +     C2H6-CH» 
Ethyl  iodide.  Methyl  iodide.        Zinc  iodide.  '  Propane. 

We  find,  then,  that  the  atoms  of  carbon  are  able  to  combine  to- 
gether; that  they  form  complex  systems  in  which  each  carbon  atom 
is  accompanied  by  atoms  of  hydrogen  or  some  other  element. 
As  we  have  done  before,  we  may  compare  the  carbon  atoms  to 
stars  or  suns  which  revolve  around  each  other ;  each  sun  is  ac- 


180  LESSONS    IN    CHEMISTRY. 

companied  by  its  own  planets,  and  we  shall  presently  see  that 
each  of  the  planets  may  have  its  satellites. 

By  reason  of  the  property  of  combination  between  its  own 
atoms,  a  property  which  is  not  possessed  in  the  same  degree  by 
the  atoms  of  any  other  element,  carbon  forms  an  almost  infinite 
number  of  compounds.  These  compounds  differ  from  those  of 
the  other  elements  in  this  respect : — while  any  other  element  forms 
a  few  compounds  with  nearly  all  other  elements,  carbon  forms  in- 
numerable compounds  containing  very  few  of  the  other  elements. 
The  more  numerous  of  the  carbon  compounds  contain  only  carbon, 
hydrogen,  oxygen,  and  nitrogen,  but  all  of  the  other  elements 
may,  under  proper  conditions,  be  made  to  form  part  of  these  com- 
pounds. The  carbon  compounds  have  been  commonly  called  or- 
ganic compounds. 

285.  The  compounds  containing  carbon  and  hydrogen  only,  are 
called  hydrocarbons ;  we  have  just  studied  three  of  them,  and  in 
the  molecules  of  each  of  these  the  combining  power  of  the  car- 
bon atoms  is  completely  exhausted.  We  may  express  in  detail 
the  atomic  relations  of  the  three. 

H  H  H  H  H  H 

H-C-H  H-C-C-H  H-C-C-C-H 

H  H  H  HUH 

Methane.  Ethane.  Prop.ane. 

The  union  of  the  carbon  atoms  together  does  not  stop  with  propane,  for  in 
turn  one  of  its  hydrogen  atoms  may  be  replaced  by  a  methyl  group,  and  the 
hydrocarbon,  C4H10,  is  the  result.  In  the  same  manner  this  may  be  converted 
into  C5H12,  and  a  whole  series  of  saturated  hydrocarbons  has  been  obtained. 
When  we  examine  the  composition  of  the  members  of  this  series,  we  see  that 
each  contains  two  more  than  twice  as  many  atoms  of  hydrogen  as  it  does  of 
carbon.  We  may  express  the  composition  of  any  member  of  the  series  by  the 
general  formula  CnH2n  +  2,  n  representing  the  number  of  carbon  atoms  in  the 
molecule.  The  names  of  these  compounds  end  in  ane,  and  after  the  fourth 
member,  the  prefix  indicates  the  number  of  carbon  atoms  in  a  molecule. 

CH*,     Methane.  C5H12.  Pentane. 

C2H<5,    Ethane.  C6!!1*,  Hexane. 

C3H8,    Propane.  C7fli6,  Heptane. 

C*H10,  Butane.  C8H18,  Octane. 

The  first  five  are  gases  at  ordinary  temperatures;  the  others  are  liquids  of 
which  the  boiling  points  are  higher  as  the  number  of  carbon  atoms  in  the 


PETROLEUM.  181 

m<  lecule  increases,  until,  when  this  number  reaches  sixteen,  the  compounds 
an  solid  at  ordinary  temperatures.  Ordinary  paraffin  is  a  mixture  of  the  solid 
numbers  of  the  series;  its  name,  meaning  poor  affinity,  indicates  that  it  does 
no;  readily  enter  into  chemical  reactions,  and,  since  this  property  is  common 
to  ill  of  the  saturated  hydrocarbons,  the  series  CnH2n  +  2  is  often  called  the 
pa  affin  series. 

>VG  see  that  each  member  of  this  series  contains  one  atom  of  carbon  and  two 
att  ms  of  hydrogen  more  than  the  preceding.  Compounds  which  thus  differ 
fn  m  each  other  by  CH2,  or  a  multiple  of  that  symbol,  and  which  have  the 
sa  ic  general  chemical  properties,  are  said  to  be  homologous,  and  to  form  a 
ho  uologous  series. 


LESSON    XXXV. 
COMPOUNDS  OF   CARBON   AND   HYDROGEN  (2). 

286.  Petroleum. — Petroleum,  or  rock-oil,  as  the  name  signi- 
fic  s,  has  been  known  from  very  early  history,  but  it  has  been 
m  irvellously  abundant  in  commerce  only  since  1859,  when  it  was 
fo  md  that  the  oil  would  flow  from  wells  bored  into  the  rock  in 
Northwestern  Pennsylvania.  The  oil  usually  occurs  in  a  loose, 
co  irse  sandstone  into  which  it  has  drained  from  its  source  in  other 
ro>;ks.  That  source  is  still  a  matter  of  uncertainty,  but  the  oil 
has  doubtless  been  formed  by  the  decomposition  of  vegetable  and 
pe  -haps  animal  matters,  long  buried  in  the  earth.  The  depth  to 
wl  ich  the  wells  must  be  sunk  varies  with  each  locality ;  some- 
times it  is  only  a  few  feet ;  sometimes  it  may  be  two  or  three 
thousand  feet.  Sometimes  the  oil  begins  to  flow  as  soon  as  the 
oil  bearing  rock  is  penetrated,  but  more  usually  the  interior  press- 
ure is  not  strong  enough  to  raise  the  oil,  and  a  pump  must  then  be 
employed.  Petroleum  is  widely  distributed ;  there  are  few  por- 
tions of  the  world  where  it  is  not  found,  and  there  are  immense 
oil -fields  in  Austria  and  Russia. 

Crude  petroleum  varies  in  color  from  pale  yellow  to  almost 
bhick  ;  it  usually  has  a  greenish  tint.  It  is  sometimes  quite  fluid, 
sometimes  thick  like  molasses.  Its  density  is  comprised  between 
0.75  and  0.92.  It  is  a  mixture  of  a  large  number  of  hydrocarbons, 

16 


182  LESSONS    IN    CHEMISTRY. 

all  of  which,  with  trifling  exceptions,  belong  to  the  class  of  par- 
affins which  we  have  just  studied.  Indeed,  all  the  saturated 
hydrocarbons,  from  CH*  up  to  C16H34,  have  been  separated  from 
coal-oil,  as  petroleum  is  commonly  called.  These  compounds  have 
diiferent  boiling  points,  and  by  slowly  raising  the  temperature  the 
most  volatile  pass  off  and  can  be  condensed  first.  In  the  manu- 
facture, the  oil  is  slowly  heated  to  about  70°,  and  the  portion 
which  distils  over  is  called  naphtha;  the  temperature  is  then 
raised  to  about  150°,  and  the  liquid  condensed  up  to  that  point 
is  benzine:  between  150°  and  280°,  kerosene,  or  illuminating  oil, 
distils  over,  and  that  portion  which  passes  between  280°  and  400° 
is  paraffin  oil  or  lubricating  oil.  Much  paraffin  distils  towards 
the  close  of  the  operation,  and  a  residue  of  coke  remains  in  the 
retort. 

Naphtha  has  a  density  of  about  0.65,  and,  when  purified  from 
its  most  volatile  constituents,  forms  gasoline,  used  in  some  gas- 
machines.  Air  is  blown  through  the  gasoline,  and  becomes  charged 
with  sufficient  of  the  vapor  of  the  volatile  hydrocarbons  to  burn 
with  an  illuminating  flame.  Benzine  has  a  density  of  about  0.702, 
and  boils  at  about  148°.  It  is  used  for  dissolving  oils  and  fats,  and 
instead  of  turpentine  for  mixing  with  paints. 

Kerosene  should  contain  no  product  whose  boiling  point  Js 
below  150°,  for  the  vapors  of  the  more  volatile  hydrocarbons  form 
dangerously  explosive  mixtures  with  air.  The  fire-test  by  which 
the  safety  of  the  oil  is  determined,  is  made  by  slowly  heating  the 
oil  in  a  little  dish  on  a  water-bath,  carefully  observing  by  means 
of  a  thermometer  the  temperature  at  which  inflammable  vapors 
are  given  off  and  the  temperature  at  which  the  oil  takes  fire. 
A  lighted  match  is  passed  rapidly  over  the  oil,  about  half  a  cen- 
timetre from  its  surface ;  when  the  vapor  burns  with  a  little 
flash,  the  thermometer  marks  the  flashing  point.  A  few  degrees 
above  this,  the  oil  itself  takes  fire.  The  flashing-point  should  not 
be  below  60°,  and  the  burning-point  not  below  65°. 

287.  Paraffin. — The  name  paraffin  is  commonly  applied  to 
that  product  of  the  distillation  of  petroleum  which  solidifies  on 
cooling :  it  is  also  a  product  of  the  destructive  distillation  of  peat 


UNSATURATED  HYDROCARBONS.  183 

and  some  kinds  of  coal.  When  the  last  liquid  portions  of  the  dis- 
tillate of  petroleum  are  cooled  by  ice,  a  considerable  quantity  of 
paraffin  separates.  When  purified,  paraffin  is  a  colorless,  trans- 
parent, or  translucent  mass.  It  is  a  mixture  of  several  members 
of  the  series  of  saturated  hydrocarbons.  Accordingly  as  it  has 
b«  ^n  prepared  and  purified,  its  melting-point  varies  from  45°  to 
6"  °.  It  makes  excellent  candles. 

288.  We  have  now  learned  something  about  one  class  of  hydrocarbons,  a 
cl   ss  in  which  the  carbon  atoms  cannot  combine  with  any  other  atoms  unless 
th  >y  separate  from  each  other.     It  is  worthy  of  notice  that  they  do  not  sepa- 
r;i  e  from  each  other  except  by  the  action  of  the  most  energetic  agents :  on  the 
C(  itrary,  these  carbon  atoms  remain  combined,  and,  with  as  many  of  their 
at  -ompanying  hydrogen  atoms  as  we  permit  to  remain  with  them,  constitute 
fi   ed  and  definite  radicals,  which  act  exactly  like  the  atoms  of  elements  having 
tl  3  same  combining  powers.     We  have  noticed  two  of  these  radicals,  methyl 
ai  d  ethyl.     In  order  that  there  may  be  a  uniformity  of  names  for  these  com- 
p  >x  groups,  chemists  have  agreed  to  retain  the  first  syllable  of  the  name  of 
tl  u  saturated  hydrocarbon,  in  the  names  of  all  compounds  derived  from  that 
h    drocarbon.     The  termination  in  yl  has  been  selected  for  the  radicals  which 
w  ;  consider  are  formed  by  the  removal  of  one  atom  of  hydrogen  from  a  satu- 
r;  ted  hydrocarbon,  and  then  the  first  word  of  the  name  of  a  compound  will 
si  ow  us  the  hydrocarbon  radical  in  the  molecule,  and  the  last  word  must  indi- 
c;  te  the  atom  or  group  of  atoms  combined  with  that  radical.     We  may  then 
in  derstand  the  composition  of  the  following  bodies: 

C'l*,    Methane.     CH3Br,        Methyl  bromide.         CIROH.    Methyl  hydrate. 
C- lie,  Ethane.        C2H5C1,        Ethyl  chloride.  C2H5.OII,  Ethyl  hydrate. 

C:H8,  Propane.      C3I1T  NH*,  Propyl  amine.  (C31F)20,  Propyl  oxide. 

When  we  have  once  acquired  definite  ideas  of  what  is  meant  by  a  radical, 
that  it  is  a  group  which  acts  precisely  as  an  atom,  having  continually  the  same 
combining  power  or  atomicity,  leaving  one  molecule  and  entering  another  as  a 
distinct  existence;  then  the  structure  of  these  complex  molecules  becomes  per- 
fectly intelligible,  and  we  need  only  be  acquainted  with  the  radicals  concerned 
in  order  to  be  able  at  once  to  interpret,  by  our  system  of  atomic  groupings,  the 
relations  of  the  atoms  in  the  molecule  of  any  compound. 

289.  Unsaturated  Hydrocarbons. — We  have  mixed  in  a  glass 
flisk  some  alcohol  with  four  times  its  weight  of  strong  sulphuric 
acid,,  and,  as  this  mixture  sometimes  froths  very  much  when  we 
heat  it,  we  have  put  in  enough  sand  to  absorb  the  liquid  almost 
entirely.     After  fitting  to  our  flask  a  cork  through  which  pass  a 
delivery- tube,  and  a  safety-tube  in  which  we  put  a  little  mercury 


184  LESSONS   IN   CHEMISTRY. 

or  some  sulphuric  acid,  we  heat  it  on  a  sand-bath.  A  gas  is  dis- 
engaged, and  we  may  collect  it  in  jars  over  the  pneumatic  trough. 

290.  ETHYLENE,  C2H4. — The  gas  which  we  have  prepared  i«  a 
hydrocarbon.  It  is  colorless  and  almost  odorless  :  its  density  com- 
pared to  air  is  0.9784,  or  compared  to  hydrogen,  14.  Analysis 
shows  that  it  contains  carbon  and  hydrogen  in  the  proportion  of 
one  atom  of  the  first  to  two  atoms  of  the  second,  and  its  density 
shows  that  its  molecule  must  contain  two  atoms  of  carbon  and  four 
of  hydrogen.  Its  composition  is,  then,  C2H4 :  it  is  called  ethylene. 
It  burns  with  a  brilliant  flame. 

Into  a  jar  of  this  gas  we  pour  a  little  bromine,  and  cause  it  to 
flow  over  the  sides  of  the  jar :  the  color  of  the  bromine  disappears, 
and  drops  of  an  oily  liquid  are  formed.  This  liquid  has  a  pleasant 
odor,  very  different  from  the  suffocating  vapor  of  the  bromine. 
The  ethylene  has  combined  with  the  bromine  and  formed  this 
liquid,  which  is  called  ethylene  bromide.  The  vapor-density  and 
analysis  of  the  compound  assign  to  its  molecule  the  composition 
C2H4Br2.  Evidently  if  the  molecule  C2H4  can  combine  directly 
with  two  atoms  of  bromine,  it  must  be  a  diatomic  molecule,  capable 
of  manifesting  the  combining  power  of  two  atoms  of  hydrogen. 
Let  us  study  the  reaction  by  which  ethylene  is  formed :  alcohol  is 
ethyl  hydrate,  C2H5.OH :  sulphuric  acid,  by  its  strong  affinity  for 
water,  converts  it  into  H20  -f  C2H4.  Then,  in  losing  the  mon- 
atomic  hydroxyl  group  and  an  atom  of  hydrogen,  the  carbon  atoms 
of  alcohol  must  recover  the  combining  powers  of  two  atoms  of 
hydrogen :  this  combining  power  is  manifested  in  the  combination 
of  ethylene  with  bromine,  chlorine,  etc.  If  two  atoms  of  hydrogen 
were  removed  from  a  molecule  of  methane,  CH4,  the  remaining 
group,  CH2,  would  be  diatomic,  and  we  believe  that  a  molecule  of 
ethylene  gas  is  formed  by  the  union  of  two  such  diatomic  groups, 
and  is  expressed  by  the  formula  CH2  CH2 ;  but  these  atoms 
then  possess  more  energy  than  when  combined  in  the  gas  ethane, 
CH3-CH3,  and  may  develop  that  energy  and  enter  into  direct  com- 
bination with  bromine,  forming  ethylene  bromide,  CH2Br— CH2Br. 

ETHYLENE  CHLORIDE,  CH2C1-CH2C1,  is  formed  when  equal 
volumes  of  chlorine  and  ethylene  are  mixed  in  diffuse  daylight. 


DIATOMIC    HYDROCARBONS.  185 

It  is  a  somewhat  oily  liquid,  and  from  this  character  ethylene  was 
fi-st  called  olefiant  gas.  It  boils  at  82°. 

ETHLYENE  BROMIDE,  CH2Br-CH2Br,  is  made  by  passing  ethy- 
Kne  gas  into  cooled  bromine.  It  boils  at  131°. 

291.  We  have  seen  that  chlorine  is  capable  of  replacing  the 
hydrogen  of  ethane,  C2H6,  atom  for  atom.  From  the  products  of 
this  reaction  we  can  by  careful  operations  separate  two  liquids 
1  i:\ving  the  composition  C2fl*Cl2,  but  having  entirely  different 
I  coperties.  These  compounds  are  isomeric,  and  we  may  understand 
t  leir  isomerism  when  we  see  that  both  atoms  of  chlorine  may 
i  -place  hydrogen  atoms  which  are  in  relation  to  the  same  atom 
of  carbon,  forming  the  molecule  CH3-CHC12;  or  each  may  replace 
a  i  atom  of  hydrogen  from  a  group  CH3;  the  compound  formed 
i  i  the  latter  case  would  of  course  be  ethykne  chloride. 

292.  Ethylene  is  only  the  first  member  of  a  long  series  of  hydrocarbons 
A  hich  we  may  consider  are  derived  from  it  by  the  replacement  of  one  or  more 
i  :'  its  hydrogen  atoms  by  the  monatomic  hydrocarbon  radicals  which  we  have 
;  i  ready  studied.     Each  of  the  compounds  so  formed  is  diatomic:  it  will  coin- 
I  ine  directly  with  two  atoms  of  chlorine  or  bromine,  and  may  be  made  to 
(  nnbine  with  two  monatomic  radicals  or  with  one  diatomic  radical.    The  names 
i  :'  these  diatomic  hydrocarbons  are  made  to  correspond  with  the  saturated 
1  ydrocarbons,  from  which  we  may  consider  they  are  derived  by  the  removal 
<  f  two  atoms  of  hydrogen,  but  the  ane  of  the  name  is  changed  to  ylene.    Ethy- 
1  me  corresponds  to  ethane,  butylene  corresponds  to  butane.     We  have  here 
o.ir  second  series  of  homologous  compounds,  each  differing  from  the  next  by 
CH2. 

C2H4,  Ethylene.  C5H10,  Amylene  or  pentylene. 

C3H6,  Propylene.  C6H12,  Hexylene. 

C*H8,  Butylene.  CrH14,  Heptylene,  etc. 

On  examination,  we  notice  that  each  molecule  contains  twice  as  many 
atoms  of  hydrogen  as  of  carbon  ;  the  general  formula  for  the  series  is  CnH2n. 
The  proportion  of  hydrogen  and  carbon  is  the  same  in  each  member  of  the 
series,  but  the  molecular  weights,  nnd  consequently  the  number  of  atoms  in 
the  molecules,  are  not  the  same.  Bodies  of  which  the  molecules  contain  the 
same  atoms  in  the  same  proportion  but  in  different  numbers  are  said  to  be 
polymeric.  All  of  these  diatomic  hydrocarbons  are  polymeric  ;  the  number 
of  carbon  atoms  and  hydrogen  atoms  in  each  is  an  exact  multiple  of  CH2. 
Because  these  hydrocarbons  combine  directly  with  chlorine  and  bromine, 
forming  oily  liquids,  the  series  is  often  called  the  olefin  series. 

293.  It  has  been  said  that  we  may  consider  these  bodies  as  formed  from 
ethylene  by  the  replacement  of  hydrogen  atoms  by  the  monatomic  radicals, 


186  LESSONS    IN    CHEMISTRY. 

methyl,  ethyl,  etc.  We  must  see  that  this  replacement  may  yield  many  in- 
stances of  isomerism.  If  one  of  the  hydrogen  atoms  of  ethylene  be  replaced 
by  methyl,  we  obtain  propylene. 

CR2--CH*  CH2-CH-CU» 

Ethylene.  Propylene. 

By  the  replacement  of  two  of  the  hydrogen  atoms  by  methyl,  we  may 
obtain  two  different  butylenes,  according  to  the  positions  of  the  replaced  hydro- 
gen atoms,  and  there  is  still  a  third  butylene,  formed  by  the  replacement  of 
one  hydrogen  atom  by  an  ethyl  group. 

CH2  CH.CH3  C(CH3)2  CH(C2H5) 

CH2  CH.CH3  CH2  CH2 

Ethylene.    (a)  Dimethylethylene.  (/3)  Dimethylethylene.        Ethylethylene. 
All  these  hydrocarbons  have   been  obtained  and  studied,  and  their  names 
indicate  the  molecules  from  which  they  are  derived  and  the  radicals  which 
are  substituted  for  the  hydrogen  atoms  in  those  molecules. 

We  can  understand  that  after  the  third  member  of  the  series  of  saturated 
hydrocarbons,  a  similar  isomerism  must  exist  for  those  compounds  also. 


LESSON    XXXVI. 

COMPOUNDS  OF  CARBON  AND  HYDROGEN  (3).— 
ANALYSIS  OF  CARBON  COMPOUNDS. 

294.  The  tar  which  condenses  during  the  distillation  of  bitu- 
minous coal  for  the  manufacture  of  gas,  is  an  exceedingly  com- 
plex liquid,  consisting  principally  of  compounds  of  carbon  and 
hydrogen.  Some  of  these  compounds  are  solid,  some  of  them  are 
volatile  liquids.  Since  they  boil  at  different  temperatures,  they 
can  be  separated  from  each  other  by  a  process  called  fractional 
distillation.  When  a  mixture  of  liquids  having  different  boiling 
points  is  distilled  very  slowly,  the  most  volatile  portions  pass  off 
first  and  may  be  condensed.  In  practice,  the  boiling  is  not  con- 
ducted very  slowly,  but  the  mixed  vapors  of  the  substances  are 
passed  through  a  tube  or  pipe  which  is  maintained  at  the  boiling 
point  of  the  most  volatile  constituent  of  the  mixture :  in  this  tube 
the  liquids  having  higher  boiling  points  are  condensed,  and  flow 
back  into  the  still,  while  the  vapor  of  the  more  volatile  liquid 


BENZOL. 


187 


parses  on  and  is  condensed  separately.  The  most  simple  apparatus 
which  we  can  employ  in  the  laboratory  is  a  rather  wide  tube  on 
which  a  couple  of  bulbs  are  blown;  this  is 
placed  vertically  in  the  flask  in  which  we  boil 
UK  mixed  liquid  (Fig.  88).  The  lower  part  of 
tin;  tube  becomes  heated  to  the  temperature  of 
th-'  mixed  vapor,  which  is  between  the  boiling 
pouts  of  the  liquids:  as  some  of  the  most 
eaily  condensed  vapor  is  cooled  to^  the  con- 
densing point,  and  converted  into  a  liquid,  the 
temperature  of  the  tube  gradually  falls  as  the 
vaoors  approach  the  upper  portion,  and  by 
carefully  regulating  the  boiling,  only  the  most 
vc  atile  liquid  passes  from  the  apparatus,  and 
th  s  is  indicated  by  a  thermometer  of  which 
th  3  bulb  is  opposite  the  short  side-tube. 

295.  Benzol,  C6H6.— The  most  volatile  con- 
stituent  of  coal-tar  is  a  liquid  called  benzol. 
It  freezes  at  5.5°,  and  boils  at  80.5°.     It  does 
not  dissolve  in  water,  but  is  soluble  in  alcohol 
an  1  ether.     It  is  very  inflammable,  and  burns 
wr.h  a  bright  but  smoky  flame.     The  com- 
position of  its  molecule  is  C6H6,  and  yet  in  most  of  its  reactions 
it  ;»cts  like  a  saturated  hydrocarbon.     We  put  a  few  crystals  of 
iodine  into  some  benzol  in  a  glass  flask,  and  pass  chlorine  through 
th<!  liquid ;  hydrochloric  acid  gas  is  given  off, 
and  the  hydrogen  atoms  of  the  benzol  are  re- 
placed by  chlorine. 

+     Cl2    =    C6H5C1     +     HC1 


FIG. 


The  iodine  only  aids  in  the  reaction  by  help- 
ing to  break  up  the  molecules  of  chlorine.  HC 


CH 


Evidently  the  molecular  structure  of  benzol  must  be 
different  from  that  of  the  other   hydrocarbons  which 
we  have  studied,  and  we  can  only  account  for  its  re- 
semblance to  the  saturated  hydrocarbons  by  supposing  th;it  its  carbon  atoms 
aie  differently  related.     Of  several  theories  which  have  been  proposed  in  order 


188 


LESSONS    IN    CHEMISTRY. 


to  explain  the  reactions  of  benzol,  we  need  only  consider  one,  which  supposes 
that  these  atoms  form  a  complex  system,  in  which  each  carbon  atom  is  com- 
bined with  three  other  carbon  atoms,  so  leaving  one  atomicity  of  each  free 
to  combine  with  an  atom  of  hydrogen  or  other  element.  We  may,  by  our 
formulae,  represent  this  arrangement  in  the  form  of  a  triangular  prism,  a 
carbon  atom  being  placed  at  each  angle. 

296.  All  the  hydrogen  atoms  of  benzol  may  be  replaced  by 
other  atoms  or  radicals,  and,  when  more  than  one  is  so  replaced, 
we  have  interesting  isomeric  compounds,  the  isomerism  depending 
on  the  relations  of  the  carbon  atoms  whose  hydrogen  atoms  are 
aifected.  Let  us  suppose,  for  example,  that  two  hydrogen  atoms 
are  replaced  by  two  chlorine  atoms :  experiment  has  shown  that 
three  compounds  may  then  be  formed,  having  precisely  the  same 
composition,  but  different  properties. 

We  can  interpret  this  by  our  theory  and  our  representation  of  the  molecule, 
by  considering  that  while  one  atom  of  chlorine  always  occupies  the  same- place, 
the  position  of  the  other  varies. 


HC 


CH        HC 


CC1 


CC1 


CH 


While  our  time  will  not  permit  the  further  development  of  those  ideas,  we 
may  say  that  theory  indicates  only  three  positions  in  which  the  two  chlorine 
atoms  can  form  entirely  different  molecules.  By  different  methods  chemists 
have  always  succeeded  in  producing  three  isomeric  compounds  in  which  two 
atoms  of  hydrogen  of  benzol  are  replaced  by  the  same  atoms  or  radicals,  but 
they  have  never  been  able  to  obtain  more  than  three  such  compounds. 

297.  There  are  many  hydrocarbons  which  we  believe  to  be 
derived  from  benzol  by  the  replacement  of  its  hydrogen  atoms  by 
radicals,  such  as  methyl,  ethyl,  etc.  Some  of  these  have  been 
obtained  by  methods  which  allow  no  doubt  as  to  their  constitu- 
tion ;  others  have  not  yet  been  so  formed,  but  certain  of  their 
chemical  reactions  seem  to  show  that  they  also  are  derived  from 
benzol.  These  hydrocarbons  and  many  of  the  bodies  derived 


TURPENTINE. — NAPHTHALINE.  189 

from  them  have  peculiar  aromatic  odors,  and  for  this  reason  the 
whole  series  of  compounds  which  are  considered  as  benzol  deriva- 
tives is  commonly  called  the  aromatic  series.  Of  these  com- 
pounds we  can  consider  only  a  few. 

298.  Methyl-benzol,  C6B5.CH3,  is  generally  called  toluol,  be- 
cause it  was  first  derived  from  tolu  balsam.     It  is  now  obtained 
fn.  in  coal-tar,  and  usually  constitutes  a  considerable  proportion  of 
thi   benzol  of  commerce.     It  is  a  colorless  liquid,  boiling  at  111°. 

Ve  can  understand  that  there  may  be  four  isomeric  compounds  formed  by 
the  replacement  of  a  single  hydrogen  atom  of  methyl-benzol,  for  that  replace- 
111  f  it  may  affect  either  a  hydrogen  atom  in  one  of  three  places  in  the  benzol 
gix  up,  C6H5,  or  a  hydrogen  atom  of  the  radical  methyl,  CH3. 

'  he  three  isomeric  dimethyl  benzols,  C6H4(CH3)2,  are  called  xylols :  two  are 
liq  .ids,  and  one  is  a  solid.  Isomeric  with  them  is  also  ethyl-benzol,  C6H5.C2H5. 

299.  Oil  of  Turpentine,  C10H16,  is  a  derivative  of  benzol,  and 
it   s  isomeric  with  a  large  number  of  essential  oils.     The  oils  of 
lei  ion,  orange,  bergamot,  juniper,  lavender,  and  many  others,  all 
ap  >ear  to  have  the  same  molecular   composition,  and  we  must 
be  ieve  that  their  differences  are  due  to  a  different  arrangement 
of  :he  atoms  constituting  their  molecules.     These  oils  are  obtained 
by  distilling  with  water  the  leaves  or  other  parts  of  the  plant  con- 
tai  ling  them.  It  is  true  that  the  boiling  point  of  each  of  these  oils 
is    uuch  higher  than  that  of  water,  but  the  steam  of  the  water 
readily  carries  over  the  oil.      The  condensed   liquid   then   sepa- 
rates into  two  layers,  the  lower  being  water,  and  the  upper  and 
lighter  being  the  essential  oil.     Oil  of  turpentine  is  so  made  by 
disLilling  with  water  the  crude  turpentine  which  flows  from  in- 
cisions made  in  certain  species  of  pine-trees.     There  are  several 
varieties  of  this  oil,  which  differ  according  to  the  species  of  pine- 
tree  which  furnishes  them.     The  density  is  about  0.87,  and  they 
boil  at  about  156°.     Oil  of  turpentine  and  most  of  the  essential 
oils  slowly  absorb  oxygen  from  the  air,  and  are  converted  into 
various  resins. 

300.  Naphthaline,  C10H8,  is  a  solid  hydrocarbon  derived  from 
coal-tar.     It  usually  occurs  as  pearly  scales,  melting  at  79°,  and 
boiling  at  218°.     It  does  not  dissolve  in  water,  and  but  slightly 
in  cold  alcohol.     It  is  soluble  in  boiling  alcohol,  and  crystallizes 


190  LESSONS    IN    CHEMISTRY. 

when  the  solution  cools.  It  is  employed  for  the  manufacture  of 
numerous  beautiful  dye-stuffs,  analogous  to  the  aniline  dyes,  which 
we  will  presently  study. 

It  will  be  noticed  that  naphthaline  is  isomeric  with  the  three  xylols  and  with 
ethyl  benzol,  and  makes  the  fifth  hydrocarbon  of  the  composition  C10I18. 

301.  Anthracene,  C14H10,  is  one  of  the  least  volatile  hydro- 
carbons obtained  from  coal-tar.  When  pure,  it  forms  beautiful 
transparent  prisms,  which  melt  at  213°  and  boil  at  about  360°. 
It  is  employed  for  the  manufacture  of  alizarin,  a  red  coloring 
matter  which  was  until  within  a  few  years  obtained  only  from 
madder.  The  ability  to  produce  this  dye-stuff  by  purely  chemical 
processes  has  permitted  large  areas  of  land  which  were  formerly 
devoted  to  the  cultivation  of  the  madder-plant  to  be  used  for 
raising  grain.  Besides  this,  chemists  have  been  able  to  prepare 
from  this  same  alizarin  valuable  dye-stuffs  of  other  colors,  and 
there  is  now  a  whole  series  of  anthracene  coloring  matters. 

ANALYSIS  OF  CARBON  COMPOUNDS. 

302.  The  proportions  in  which  the  elements  exist  in  any  carbon  compound 
are  determined  by  elementary  analysis.  If  the  compound  contains  other  ele- 
ments than  carbon,  hydrogen,  and  oxygen,  its  analysis  requires  several  opera- 
tions :  if  only  these  three  elements  be  present,  the  carbon  and  hydrogen  are 
determined  by  one  operation,  and  the  quantity  of  oxygen  is  the  difference  be- 
tween the  sum  of  the  carbon  and  hydrogen  and  the  total  weight  of  the  substance 
analyzed.  The  nnalysis  is  conducted  by  mixing  a  weighed  quantity  of  the 
substance  with  pure  and  dry  cupric  oxide  in  a  long  glass  tube,  one  end  of 
which  is  drawn  out  to  a  fine  point  and  sealed.  The  other  end  is  connected 
with  a  small  U-tube  containing  pumice-stone  wet  with  sulphuric  acid,  and  the 
U-tube  is  connected  with  a  bulbed  tube  containing  a  solution  of  potassium 
hydrate  (Fig.  89).  The  tube  is  heated  to  redness  in  a  long  tube-furnace,  and 
the  oxygen  of  the  cupric  oxide  converts  the  hydrogen  of  the  carbon  com- 
pound into  water,  while  the  carbon  is  burned  into  carbon  dioxide.  The  water 
is  absorbed  in  the  tube  containing  the  pumice  and  sulphuric  acid,  while  the 
carbon  dioxide  is  absorbed  by  the  potassium  hydrate.  Towards  the  close  of 
the  operation,  a  caoutchouc  tube  connected  with  an  oxygen  gas-holder  is 
slipped  over  the  drawn-out  point  of  the  combustion-tube ;  the  oxygen  is  turned 
on,  and  the  point  is  broken  ofi°  by  pinching  the  end  of  the  tube.  A  current  of 
pure  dry  oxygen  is  then  passed  through  the  red-hot  tube,  and  all  traces  of 
carbon  dioxide  and  watery  vapor  are  forced  through  the  absorption-tubes;  at 
the  same  time  any  unburned  carbon  is  completely  consumed,  and  the  copper 
from  which  oxygen  has  been  removed  is  again  converted  into  cupric  oxide 


ANALYSIS    OF   CARBON    COMPOUNDS. 


191 


LESSONS    IN    CHEMISTRY. 

for  another  operation.  The  increased  weight  of  the  U-tube  (j  and  g),  in  which 
water  has  been  absorbed,  is  due  to  the  water,  and  one-ninth  of  the  increase 
will  represent  the  quantity  of  carbon  in  the  amount  of  substance  analyzed. 
The  increased  weight  of  the  bulbed  tube  (h)  is  due  to  carbon  dioxide,  anJ 
if'  or  A>  °*  tnis  increase  W'H  give  us  the  quantity  of  carbon  which  we  wish  to 
determine.  Since  the  current  of  oxygen  would  carry  a  little  vapor  of  water 
out  of  the  bulbed  tube,  and  so  diminish  its  weight,  a  small  tube  (?)  containing 
pumice  and  sulphuric  acid  is  attached,  and  in  this  the  vapor  is  retained;  this 
tube  is  always  weighed  with  the  potash  bulbs. 

Having  determined  the  proportions  of  all  the  elements  in  a  compound,  its 
molecular  weight  is  calculated  from  its  vapor-density,  or,  if  this  be  not  pos- 
sible, by  indirect  methods.  Knowing  the  molecular  weight  and  the  propor- 
tion of  each  element  present,  it  is  very  easy  to  fix  the  chemical  formula 
expressing  the  composition  of  the  molecule. 


LESSON    XXXVII. 
ALCOHOLS  (i). 

303.  When   the  iodide  of  a  radical  like   methyl  or  ethyl  is 
heated  with  silver  oxide  and  water,  silver  iodide  is  formed,  and 
the  iodine  of  the  carbon   compound   is  replaced  by  a  hydroxyl 
group. 

2CH3I         +         Ag2Q        +       H2Q      =      2AgI         +         2CH3.0H 
Methyl  iodide.          Silver  oxide.  Silver  iodide.  Methyl  hydrate. 

A  hydrate  of  the  hydrocarbon  radical  is  so  formed,  and  these 
hydrates  constitute  what  are  called  the  alcohols.  We  must  study 
some  of  the  more  important  of  these  compounds. 

304.  Methyl  Alcohol,  CFP.OEL—  The  liquid  which  condenses 
during  the  manufacture  of  charcoal  (§  226)  contains  small  quan- 
tities of  a  volatile  liquid  which  can  be  separated  by  careful  frac- 
tional distillation.     This  liquid  is  usually  sold  under  the  name 
methylene  or  wood-spirit.     It  is  impure  methyl  alcohol,  and  is 
used  for  the  manufacture  of  varnishes,  and  for  dissolving  fats  and 
oils.     Methyl  alcohol  has  the  property  of  forming  with  calcium 
chloride  a  crystalline  compound,  and  is  usually  purified  by  satu- 
rating the  wood-spirit  with  calcium  chloride,  and  evaporating  the 


ALCOHOLS.  193 

so  ution  by  a  gentle  heat  until  it  crystallizes.  The  crystals  are 
dissolved  in  water;  when  their  solution  is  boiled,  the  compound 
of  methyl  hydrate  and  calcium  chloride  is  decomposed,  and  the 
m  3thyl  alcohol  can  be  separated  by  fractional  distillation. 

Pure  methyl  alcohol  is  a  colorless  liquid,  of  an  odor  exactly  like 
tl  at  of  common  alcohol.  Its  density  at  0°  is  0.814,  and  it  boils 
at  66.5°.  It  mixes  in  all  proportions  with  water  and  with  ordinary 
ai  ;ohol.  It  is  inflammable,  and  burns  with  an  almost  colorless 
fl  me.  We  throw  a  piece  of  sodium  into  methyl  alcohol :  hydrogen 
i.-  given  off,  and  the  metal  dissolves  :  an  atom  of  sodium  has  re- 
p  need  the  hydrogen  atom  of  the  group  hydroxyl,  and  sodium 
u  ethylate  is  formed.  The  reaction  is  precisely  like  that  which 
y  elds  sodium  hydrate  in  the  reaction  of  sodium  with  water. 
2H-0-H  +  Na2  -  2NaOH  +  H2 

2CH3-0-II        +         Na2  2CH3-ONa         +         H2 

Methyl  alcohol.  Sodium  methylate. 

When  methyl  alcohol  is  oxidized  slowly,  an  atom  of  oxygen 
r<  places  two  hydrogen  atoms  of  the  methyl  group,  CH3,  and  formic 
a>  id  results. 

CH3.0H        +        O2  H20        +        CHO.OH 

Methyl  hydrate.  Formic  acid. 

305.  Ethyl  Alcohol,  C2H5.OH.— When  ethylene  gas  is  passed 
ii  to  strong  hydriodic  acid,  direct  combination  takes  place,  and 
ethyl  iodide  is  formed. 

C2II4     i     HI    =    C2H5I 

When  this  ethyl  iodide  is  heated  with  potassium  hydrate  solution, 
a  double  decomposition  takes  place,  yielding  potassium  iodide  and 
ethyl  alcohol. 

C2H5I     +     KOH  KI     +     C2H5.0H 

H  owever,  ethyl  hydrate,  which  is  ordinary  alcohol,  is  manufactured 
by  a  peculiar  decomposition  of  glucose,  or  some  substance  having 
the  same  composition  as  glucose.  This  decomposition  is  brought 
about  by  a  minute  organism  which  lives  and  multiplies  by  con- 
verting the  glucose  into  carbon  dioxide  and  alcohol.  A  decompo- 
sition due  to  such  an  organized  being  is  called  a  fermentation,  and 
the  organism  is  called  a  ferment.  The  molecule  of  glucose  is 
i  n  17 


194  LESSONS   IN    CHEMISTRY. 

expressed  by  the  formula  C6H1206,  and,  although  small  quantities 
of  other  substances  are  produced  during  the  fermentation,  which 
is  caused  by  the  yeast-plant  and  is  called  the  alcoholic  fermenta- 
tion, the  general  change  may  be  represented  by  the  equation 
C6H12Q6    =     2C2H5.0H     +     2C02 

For  the  manufacture  of  alcohol,  the  product  of  the  fermentation 
is  distilled,  and  the  alcohol  so  separated  from  the  water.  However, 
the  best  apparatus  does  not  give  alcohol  stronger  than  about  ninety- 
five  per  cent.  Pure  or,  as  it  is  commonly  called,  absolute  alcohol 
is  made  by  putting  quick-lime  into  the  strongest  alcohol  of  com- 
merce, and  distilling  the  mixture  after  it  has  stood  several  days. 
By  reason  of  its  strong  affinity  for  water,  the  lime  then  retains  all 
of  that  liquid. 

Pure  alcohol  is  a  colorless  liquid,  having  a  faint  but  pleasant 
odor.  Its  density  at  0°  is  0.8095,  and  it  boils  at  78.4°.  It  mixes 
with  water  in  all  proportions,  and  the  mixture  becomes  slightly 
warm  and  contracts  in  volume.  Alcohol  dissolves  many  substances 
which  are  insoluble  in  water;  among  these  are  iodine,  the  essential 
oils,  fats,  and  resins.  The  spirits  of  the  pharmacies,  such  as  spirits 
of  ammonia,  are  solutions  of  volatile  substances  in  alcohol ;  tinc- 
tures are  similar  solutions  of  non-volatile  substances. 

Alcohol  is  combustible,  and  burns  with  a  pale  flame,  the  prod- 
ucts of  the  combustion  being  carbon  dioxide  and  water. 

By  the  slow  oxidation  of  alcohol,  acetic  acid  and  a  volatile 
liquid  called  aldehyde  are  formed ;  acetic  acid  by  the  replacement 
of  two  atoms  of  hydrogen  of  the  ethyl  group  by  an  atom  of  oxy- 
gen, and  aldehyde  by  the  replacement  of  the  hydroxyl  group  and 
one  atom  of  hydrogen  by  an  atom  of  oxygen.  Water  is  of  course 
formed  in  both  cases. 

CH3-CH2.OH  f     0      =     CH3-CHO        +     H20 

Alcohol.  Aldehyde. 

CH3-CH2.OH  +     O2    ==     CH3-CO.OH     +     H20 

Alcohol.  Acetic  acid. 

The  slow  oxidation  of  alcohol  may  be  made  to  develop  consid- 
erable heat.  Over  a  little  alcohol  in  a  beaker  we  suspend  a  coil 
of  platinum  wire  which  we  have  previously  heated  to  redness 


ALCOHOL.  195 

(Fig.  90).     The  wire  becomes  bright  red,  and  will  continue  to 

"low  as  long  as  sufficient  air  and  alcohol  vapor  come  in  contact 

with  the  platinum.     At  the  temperature  of  the 

re'l-hot  wire  the  alcohol  vapor  is  fully  oxidized, 

but  if  we  remove  it,  and  allow  it  to  cool  slightly, 

and  then  withdraw  it  before  it  becomes  bright, 

wi   may  notice  the  peculiar  odor  developed  in  the 

be  iker.     This  is  in  part  due  to  the  formation  of 

al  lehyde. 

506.  The  reaction  of  alcohol  with  solutions  of  certain  metals  in  nitric  acid 
yi  Ids  a  class  of  bodies  called  the  fulminates.  Fulminating  mercury,  which  is 
u?  -d  for  charging  percussion-caps,  may  be  prepared  by  dissolving  about  two 
gr  iinmes  of  mercury  in  fifteen  cubic  centimetres  of  strong  nitric  acid  contained 
in  a  rather  large  flask  or  beaker.  The  reaction  is  aided  by  a  gentle  heat,  and 
sis  soon  as  all  the  mercury  has  disappeared,  the  vessel  is  removed  from  the 
pi  iximity  of  flame,  and  twenty  cubic  centimetres  of  alcohol  are  added.  A 
vi  lent  reaction  takes  place,  dense,  white,  poisonous  vapors  are  disengaged, 
in  I  fulminate  of  mercury  is  deposited  as  a  light-gray  powder.  When  the 
eti  -rvescence  has  ceased,  the  vessel  is  filled  with  water,  and  the  acid  liquid  is 
p<  ired  off:  the  mercuric  fulminate  is  washed  by  decantation,  until  the  water 
iii  longer  becomes  acid.  It,  is  then  collected  on  a  small  filter,  and  dried  by 
ex  oosure  to  the  air.  The  reaction  by  which  this  compound  is  formed  is  very 
co  uplicated,  but  the  composition  of  mercuric  fulminate  is  expressed  by  the 
fo  mula  HgC2N202,  and  its  molecule  is  believed  to  represent  methane,  CH4,  in 
wl  ich  the  four  atoms  of  hydrogen  are  replaced  by  a  group  NO2,  a  cyanogen 
gr  »up,  and  a  diatomic  atom  of  mercury, 

CII4,  Methane.  C(N02)(CN)Hg,  Fulminate  of  mercury. 

Culminate  of  mercury  explodes  violently  by  friction  or  percussion,  and  should 
be  kept  in  loosely-corked  bottles,  lest  it  be  exploded  by  the  friction  of  a  glass 
stopper.  It  explodes  also  at  a  temperature  of  about  180°.  Although  this  body 
is  ,;o  exceedingly  explosive  that  it  would  burst  a  gun-barrel  in  which  it  was 
detonated,  the  expansive  force  of  the  gases  produced  is  much  inferior  to  that  of 
those  disengaged  by  gunpowder,  and  it  could  not  be  used  for  projectile  effects. 

307.  ALCOHOLIC  BEVERAGES  are  products  of  the  fermentation 
of  substances  containing  glucose  or  some  body  capable  of  being 
converted  into  glucose.  In  the  manufacture  of  wine,  which  is  the 
natural  beverage  of  those  countries  in  whose  climates  the  wine- 
grapes  nourish,  the  glucose  is  derived  from  the  juice  of  the  grape : 
the  ferment  also  is  natural  to  the  grape,  for  it  is  developed  from 
the  albumen  like  matter  of  the  pulp.  Since  the  alcoholic  fermen- 


196  LESSONS    IN    CHEMISTRY. 

tation  is  a  transformation  of  glucose,  and  no  air  is  necessary  for 
the  change,  this  fermentation  may  continue  in  closed  vessels ;  in 
sparkling  wines  or  champagnes  part  of  the  fermentation  takes 
place  in  the  bottle,  and  the  carbon  dioxide  formed  is  dissolved  in 
the  liquid  under  pressure.  All  the  carbon  dioxide  has  escaped 
from  still  wines.  The  fermentation  of  apple-juice  and  the  juices 
of  other  fruits,  which  yields  cider  and  the  various  fruit-wines,  is 
quite  similar  to  the  fermentation  of  grape-juice.  Wines  contain 
from  seven  to  twenty  per  cent,  of  alcohol. 

Beer,  ale,  and  porter  are  produced  from  grain,  preferably  from 
barley.  Grain  contains  no  glucose,  but  during  the  sprouting  of 
the  grain,  a  body  precisely  similar  to  glucose  and  having  the  same 
composition  is  formed.  It  is  called  maltose.  iTie  barley  is  there- 
fore moistened  and  kept  at  a  temperature  of  about  15°  until  a 
sprout  as  long  as  the  grain  is  formed.  The  sprouting  is  then  ar- 
rested by  heating  the  grain,  which  is  now  called  malt,  to  about 
50°,  after  which  the  dry  malt  is  ground  to  a  coarse  powder  and 
is  ready  for  brewing.  It  is  then  cooked  for  several  hours  with 
water  at  a  temperature  of  50°  or  60°,  and  all  the  maltose  and 
much  of  the  nutritious  matter  of  the  malt  are  dissolved  :  the  liquid 
thus  formed  is  heated  with  hops  to  impart  an  aromatic  flavor,  and 
is  then  rapidly  cooled ;  after  a  little  yeast  is  added,  the  wort  is 
allowed  to  ferment  at  as  low  a  temperature  as  possible,  until  in  a 
few  days  beer  or  ale  is  obtained,  according  to  the  proportions  of 
substances  used. 

Beer  contains  from  two  to  five  per  cent,  of  alcohol,  and  ale  a 
somewhat  larger  proportion,  sometimes  as  high  as  ten  per  cent. 
As  there  is  in  this  country  no  government  inspection  of  malted 
liquors,  beer  is  often  adulterated  by  the  substitution  of  various 
more  or  less  injurious  bitter  substances  for  the  hops,  and  of  glu- 
cose for  a  part  of  the  malt :  glucose  is  not  injurious,  but  it  con- 
tains no  nutritious  matter,  as  is  the  case  with  malt. 

SPIRITUOUS  LIQUORS  are  not  natural  products  ;  they  are  dis- 
tilled from  various  fermented  liquids,  and  are  only  dilute  alcohol 
containing  some  flavoring  matter.  Brandy  is  distilled  from  wine ; 
whiskey  from  malted  liquors  of  all  kinds,  derived  from  corn,  rye, 


ALCOHOLS.  197 

oa:s,  and  even  potatoes;  rum  is  distilled  from  fermented  molasses 
from  sugar-cane  ;  gin  is  dilute  alcohol  flavored  with  the  essential 
oil  of  juniper-berries.  These  liquids  contain  from  forty  to  sixty 
per  cent,  of  alcohol. 


LESSON    XXXVIII. 
ALCOHOLS  (2). 

308.  Propyl  Alcohols,  C'tT.OH.— A  substance  of  this  com- 
p<  -itiou  exists  in  very  small  proportion  among  the  products  of  the 
all  oholic  fermentation.  It  is  a  liquid,  boiling  at  98°.  When  we 
ex  imine  the  composition  of  the  hydrocarbon  propane,  we  will  no- 
tic  e  that  the  three  carbon  atoms  are  not  similarly  related  :  two  are 
re  ated  to  one  other  carbon  atom,  but  the  third  is  related  to  both 
of  the  first  two. 

HHH 

H-C-C-C-H 

HHH 

Cl  emists  have  discovered  two  propyl  alcohols,  and  indeed  two 
m<  difications  of  every  compound  containing  the  radical  propyl, 
C3HT.  We  account  for  this  in  our  theory  by  considering  that  in  one 
of  these  alcohols  the  hydroxyl  group  replaces  one  of  the  hydrogen 
atoms  of  either  of  the  two  carbon  atoms  which  are  related  to  only  one 
other  carbon  atom,  and  we  see  that  all  these  atoms  of  hydrogen  are 
similarly  situated.  The  alcohol  so  formed  is  normal  propyl  alcohol, 
that  which  we  have  briefly  considered.  In  the  other  alcohol  of 
the  same  composition  the  hydroxyl  group  is  joined  to  that  carbon 
atom  which  is  related  to  two  others :  it  is  called  isopropyl  alcohol, 
and  boils  at  86°.  We  see,  then,  that  there  are  two  propyl  radi- 
cals: propyl,  CH3-CH2-CH2;  and  isopropyl,  CH(CH3)2.  Those 
alcohols  in  which  the  carbon  atom  which  holds  the  hydroxyl  group 
in  the  molecule  is  related  to  only  one  other  atom  of  carbon,  are 
colled  primary  alcohols,  Those  in  which  the  hydroxyl  group  is  in 

17* 


198  LESSONS    IN    CHEMISTRY. 

relations  with  an  atom  of  carbon  which  is  related  to  two  others, 
are  called  secondary  alcohols. 

309.  Butyl  Alcohols,  C4H9.OH.— Chemists  have  succeeded  in 
preparing  four  different  butyl  alcohols.    They  are  all  liquids,  with 
the  exception  of  one,  which  is  a  crystalline  solid,  in  whose  mole- 
cule we  believe  that  the  hydroxyl  group  is  held  by  a  carbon  atom 
which  acts  as   the  centre   of  a  system ;    around  this  atom  are 
grouped  three  other  atoms  of  carbon  and  their  accompanying  hy- 
drogen atoms.     It  is  C(CH3)3OH.     It  is  called  a  tertiary  alcohol, 
that  being  the  name  applied  to  those  alcohols  in  which  the  carbon 
atom  which  brings  the  hydroxyl  group  into  the  molecule  is  related 
to  three  other  carbon  atoms. 

310.  Amyl  Alcohols,  C5Hn.OH. — There  are  now  known  seven 
alcohols  of  this  composition.     Two  of  them  exist  in  the  oily  resi- 
due which  is  left  in  the  distillation  of  brandy  and  whiskey,  and 
they  are  therefore  products  of  the  alcoholic  fermentation  of  glu- 
cose.    This  oily  residue  is  called  fusel  oil :  it  has  a  peculiar  and 
not  altogether  pleasant  odor,  and,  besides   some  ordinary  alcohol 
which  it  still  retains,  is  a  mixture  of  propyl,  butyl,  and  two  amyl 
alcohols.     The  first  two   may  be  isolated  from  the  mixture  by 
careful  fractional  distillation,  but  for  the  separation  of  the  two 
amyl  alcohols  chemical   means  must  be  employed.      The  crude 
fusel  oil  is  a  valuable  solvent  for  many  substances,  to  dissolve 
which  ordinary  alcohol  would  otherwise,  be  required.     Butyl  and 
amyl  alcohols  do  not  mix  in  all  proportions  with  water,  as  do  ethyl 
and  propyl  alcohols. 

We  pour  small  quantities  of  methyl,  ethyl,  butyl  alcohol  from 
fusel  oil,  and  amyl  alcohol  from  fusel  oil,  into  four  separate  plates, 
and  light  them.  We  find  that  the  first  is  the  most  combustible, 
and  that  we  can  light  the  last  only  with  difficulty.  The  flame  of 
the  methyl  alcohol  is  almost  colorless,  but  the  brightness  of  the 
flames  increases  to  the  amyl  alcohol,  which  burns  with  a  bright 
light.  The  effect  of  an  increased  number  of  carbon  atoms  com- 
bined in  the  molecule  is  then  to  render  the  compound  less  volatile, 
and  more  difficult  to  inflame. 

311.  Glycols. — We   have   learned   that  when   ethylene    gas, 


GLYCERIN.  199 

C2H4,  is  passed  into  bromine,  a  direct  combination  takes  place, 
am  ethylene  bromide,  C2H4Br2,  is  formed ;  we  have  also  acquired 
some  idea  of  the  molecule  of  this  new  compound.  When  ethylene 
bn:  rnide  is  boiled  with  a  solution  of  potassium  carbonate  in  water, 
carbon  dioxide  is  given  off,  and,  in  addition  to  the  potassium 
br<  mide  which  is  formed,  the  liquid  contains  a  new  body. 

C2II4Br2  +  K2C03  +  I120  =  C2H*(OII)2  +  2KBr  +  CO2 
This  new  compound,  C2H4(OH)2,  is  formed  by  the  replacement 
of  the  two  bromine  atoms  of  ethylene  bromide  by  two  hydroxyl 
gn  ups.  It  is  called  ethylene  alcohol,  and  after  the  potassium 
br<  mide  has  crystallized  it  can  be  separated  by  careful  fractional 
distillation,  and  then  forms  a  syrupy  liquid  having  a  sweet  taste. 
Si  ice  it  is  a  neutral  body,  and  is  a  hydrate,  it  is  called  an  alcohol, 
an  1  it  is  a  diatomic  alcohol,  because  it  contains  two  hydroxyl 
gi  >ups.  It  is  the  first  member  of  a  series  of  diatomic  alcohols 
d(  'ived  from  the  hydrocarbons  of  the  series  CnH2n.  From  its 
s\\  :;et  taste,  Wurtz,  its  discoverer,  gave  it  the  name  glycol,  and  the 
di  tomic  alcohols  are  often  called  glycols. 

312.  Glycerin,  C3H5(OH)3.— The  fats  and  fatty  oils  are  corn- 
pi  x  compounds  containing  the  radicals  of  certain  carbon  acids, 
ca  led  the  fatty  acids  (§  338),  and  the  radical  of  the  well-known 
su  )stance  glycerin.  By  the  action  of  metallic  hydrates  on  these 
compounds,  atoms  of  metal  replace  the  glycerin  radical,  which  com- 
bines with  the  hydroxyl  groups  which  were  before  in  the  metallic 
hydrate  molecules.  At  high  temperatures,  steam  acts  precisely 
like  the  metallic  hydrates,  and  glycerin  is  manufactured  by  dis- 
til ing  fats  and  oils  in  a  current  of  superheated  steam  ;  that  is, 
steam  which  has  been  passed  through  very  hot  pipes.  The  radical 
of  glycerin  having  been  found  to  be  the  group  C3H5,  we  may 
represent  the  change  thus  : 

C3H6(fatty  acid  radical)3  +  3HOH  =   C3H5(OH)8  +  3H(fatty  acid  radical). 
Fat  or  Oil.  Water.  Glycerin.  Fatty  acid. 

Glycerin  is  a  colorless,  syrupy  liquid,  having  a  sweet  taste.  Its 
density  is  about  1.28.  It  freezes  at  about  0°,  and  melts  at  about 
7°.  When  it  is  heated,  it  boils  at  about  280°,  but  is  partially 
decomposed,  producing  a  very  irritating  odor  of  a  substance  called 


200  LESSONS    IN    CHEMISTRY. 

acrolein.     It  may  be  distilled  in  a  vacuum  or  in   a  current  of 
steam.     It  dissolves  in  all  proportions  of  water  and  alcohol. 

A  molecule  of  glycerin  contains  three  hydroxyl  groups  ;  glycerin 
is  then  a  triatomic  alcohol.  Each  of  these  hydroxyl  groups  may 
be  replaced  by  a  monatomic  atom  or  radical,  and  a  large  number 
of  glycerin  derivatives  have  been  so  formed. 

313.  NITROGLYCERIN,  C3H5  (NO3)3.— In  a  little  beaker  glass 
placed  in  ice-water,  we  have  prepared  a  mixture  of  equal  volumes 
of  strong  sulphuric  and  nitric  acids ;  into  this  cold  mixture  we 
pour  a  few  drops  of  glycerin,  and,  after  stirring  for  a  few  moments, 
we  throw  the  contents  of  the  beaker  into  another  glass  nearly 
filled  with  cold  water.  A  few  drops  of  an  oily  liquid  separate, 
and  fall  to  the  bottom  of  the  glass ;  we  pour  off  nearly  all  the 
water ;  then,  by  means  of  a  glass  tube  drawn  out  to  a  small  open- 
ing, we  remove  a  drop  of  the  oil,  and  place  it  on  the  corner  of  a 
piece  of  paper ;  when  we  light  this,  it  burns  with  a  bright  flash. 
We  now  allow  another  small  drop  to  fall  on  a  nearly  red-hot  piece 
of  sheet  iron  ;  it  explodes  with  a  loud  report.  We  place  another 
small  drop  on  an  anvil,  and  when  we  strike  it  with  a  hammer 
there  is  another  loud  explosion.  The  oil  is  nitroglycerin  ;  it  has 
been  formed  by  the  removal  of  three  molecules  of  water  from  one 
molecule  of  glycerin  and  three  molecules  of  nitric  acid,  and  the 
union  of  the  remaining  groups,  C3H5  and  3N03. 

C3H5(OH)3  +  3HN03  -  3H*0  +  C3H5(N03)3 
When  nitroglycerin  explodes,  carbon  dioxide  and  water  are  formed. 
The  energy  of  the  explosion  is  due  to  the  energy  of  motion  of  the 
atoms  in  a  molecule  of  nitroglycerin  being  greater  than  that  en- 
ergy in  the  carbon  dioxide,  water,  and  nitrogen,  and  during  the 
explosion  the  excess  of  energy  appears  as  heat  and  the  energy 
necessary  to  convert  the  products  into  the  gaseous  state.  Nitro- 
glycerin is  used  in  blasting  operations,  but  it  is  usually  mixed  with 
a  very  fine  sandy -earth,  and  the  mixture  is  called  dynamite.  This 
is  made  into  cartridges  which  are  exploded  by  a  fuse  and  deto- 
nating cap.  Nitroglycerin  is  not  a  safe  body  to  handle ;  for  experi- 
mental purposes  we  prepare  only  a  few  drops  of  it. 


SIMPLE    ETHERS. 


201 


LESSON    XXXIX. 
SIMPLE  ETHERS. 

-14.  Oxides  of  Hydrocarbon  Radicals,— In  a  glass  flask  we 
ha^  e  cautiously  mixed  some  methyl  alcohol 
wit  :i  about  its  own  volume  of  strong  sul- 
plr.ric  acid;  after  adapting  a  cork  and 
str  ight  tube  to  the  flask,  we  heat  it,  and 
sou  »  a  colorless  gas  is  disengaged.  We 
lig  it  the  gas,  and  it  burns  with  a  rather 
bri  :ht  flame.  (Fig.  91.)  It  is  methyl  ox- 
ide ;  the  sulphuric  acid  has  removed  a  mole- 
cui ;  of  water  from  two  molecules  of  methyl 
ale  »hol,  and  the  two  methyl  groups  are  held 
tog  3ther  by  an  atom  of  oxygen. 

2}H3.OH  (CH3)2Q  +  R2Q 

Mot  lyl  alcohol.  Methyl  oxide. 

'  'he  density  of  methyl  oxide  compared  to 
hy*  rogen  is  23.  The  gas  is  converted  into 
a  1  quid  at  a  temperature  of  — 36°.  It  is 
soluble  in  water,  alcohol,  and  ether. 

In  this  compound  we  are  again  shown  that  the  methyl  group 
acb  like  an  atom  of  hydrogen.  It  is  a  monatomic  radical,  and  its 
composition  is  like  that  of  water,  excepting  that,  instead  of  two 
atoms  joined  by  an  atom  of  oxygen,  two  groups  or  systems  are 
held  to  the  oxygen  atom. 

II-O-H  H3C-0-CH3 

Water.  Methyl  oxide. 

The  other  monatomic  radicals  form  similar  oxides,  and  these 
oxides  form  part  of  a  large  class,  called  the  simple  ethers. 

315.  ETHYL  OXIDE,  (C2H3)20. — This  compound,  which  is 
commonly  called  ether,  may  be  formed  by  a  number  of  reactions. 
In  a  strong  glass  tube  we  have  sealed  some  ethyl  iodide  and  silver 


FIG.  91. 


202 


LESSONS    IN   CHEMISTRY. 


oxide,  and  have  heated  the  tube  for  several  hours  in  boiling  water. 
We  now  find  that  the  black  color  of  the  silver  oxide  has  changed 
to  yellow,  which  is  the  color  of  silver  iodide.  A  double  decom- 
position has  taken  place,  yielding  silver  iodide  and  ethyl  oxide, 
which  we  may  recognize  by  its  odor  and  other  properties  when  we 
cut  open  the  tube. 

Ag2Q         +         2C2H5I        =         2AgI         +         (C2H5)2Q 
Silver  oxide.          Ethyl  iodide.  Silver  iodide.  Ethyl  oxide. 

In  a  rather  large  flask  we  have  mixed  some  ninety  per  cent, 
alcohol  with  one  and  four-fifths  times  its  weight  of  strong  sulphuric 
acid.  We  adapt  to  this  flask  a  cork  having  three  holes  ;  through 
one  passes  a  thermometer  (£,  Fig.  92)  ;  another  gives  passage  to  a 


FIG.  92. 


tube  through  which  we  may  allow  alcohol  to  flow  from  a  reservoir, 
while  to  the  third  is  fitted  a  delivery-tube  connected  with  a  con- 
denser through  which  flows  a  stream  of  ice-water.  We  now  heat 
the  flask  until  the  thermometer  shows  that  the  liquid  into  which 


ETHYL    OXIDE.  203 

the  bulb  dips  has  a  temperature  of  140°  ;  then  we  regulate  the 
flame  so  that  the  temperature  may  not  rise  further,  and  start  a 
ami:  11  stream  of  alcohol  from  the  reservoir.  This  alcohol  is 
qul-kly  changed  to  ether,  which,  together  with  the  water  formed, 
distils  and  collects  in  the  receiving-bottle. 

The  reaction  which  takes  place  in  this  operation  is  worth  our 
study.  When  alcohol  is  mixed  with  strong  sulphuric  acid,  water 
is  i  >rmed,  and  an  ethyl  group  is  substituted  for  one  atom  of  hy- 
dro j;en  of  sulphuric  acid,  producing  a  compound  called  ethyl  sul- 
phi.ric  acid. 

C2H5.0H     +     H2S04    =     H20     +     (C2H3)HSO* 
Alcohol.  Ethylsulphuric  acid. 

1  f  this  ethyl  sulphuric  acid  is  heated,  it  is  converted  into  sul- 
phi  ric  acid  and  ethylene  gas,  C2H* ;  if  it  is  boiled  with  water,  it 
aga  n  yields  alcohol  and  sulphuric  acid  ;  but  if  it  is  boiled  with 
an  idditional  quantity  of  alcohol,  the  result  is  sulphuric  acid  and 
eth  jr. 

(C2H5)HSO*     +     C2H5.OH     =     H2SO*     +     (C2H5)20 
Ethylsulphuric  acid.          Alcohol.  Ether. 

1  f  methyl  alcohol  be  used  instead  of  ethyl  alcohol,  a  mixed  oxide 
of  ]Qethyl  and  ethyl  is  produced. 

(C2H5)HSO*     +     CH».OH     ,       H2SO*     +     CH3-0-C2H5 

Ethyl  oxide  is  a  colorless,  very  mobile  liquid,  having  a  pleasant 
odor  and  a  somewhat  burning  taste.  Its  density  at  0°  is  0.736 ; 
it  b oils  at  34.5°.  It  will  dissolve  in  nine  times  its  weight  of  water, 
and  one  part  of  water  will  dissolve  in  thirty-six  parts  of  ether. 
Ether  dissolves  small  quantities  of  sulphur  and  phosphorus,  and 
large  proportions  of  bromine,  iodine,  fats,  oils,  and  many  other 
substances  which  are  insoluble  in  water. 

Ether  is  very  inflammable,  and  its  vapor  forms  an  explosive 
mixture  with  air.  We  suspend  a  heated  coil  of  platinum  wire 
over  a  little  ether  in  a  beaker,  as  we  made  a  similar  experiment  with 
alcohol,  and  the  slow  combustion  of  the  ether  vapor  develops  so 
much  heat  that  the  platinum  wire  becomes  hot  enough  to  inflame 
the  ether. 

The  vapor  of  ether  is  very  heavy, — 2.564  compared  to  air.     We 


204  LESSONS   IN   CHEMISTRY. 

pour  a  little  ether  into  a  warm  beaker,  and  then,  holding  the  short 
end  of  a  small  siphon  immediately  above  its  surface,  establish  a  cur- 
rent of  ether  vapor  by  drawing  out  the 
air  by  the  mouth  ;  the  heavy  ether  vapor 
continues  to  flow  through  the  siphon,  as 
would  a  liquid,  and,  when  we  light  it,  will 
burn  as  long  as  any  ether  remains  in  the 
beaker  (Fig.  93). 

The  inhalation  of  ether  vapor  produces 
anaesthesia,  and  for  this  reason  ether  is 
largely  employed  as  an  anaesthetic  in  surgi- 

cal operations. 
FIG.  93. 

The  other  monatomic  hydrocarbon  radicals  form 

oxides  corresponding  to  the  oxides  of  methyl  and  ethyl  :  each  of  these  con- 
tains two  radicals  related  to  one  atom  of  oxygen.  The  diatomic  hydrocarbons, 
ethylene  and  its  homologues,  form  oxides  containing  one  atom  of  oxygen  and 
one  molecule  of  the  hydrocarbon,  as  in  ethylene  oxide,  which  may  be  obtained 
by  heating  ethylene  bromide  with  silver  oxide. 


+         Ag'O         =  >0         +         >A«Br 

CH'Br  CH^ 

Ethylene  bromide.       Silver  oxide.        Ethylene  oxide.  Silver  bromide. 

316.  Chlorides,  Bromides,  etc.  —  The  class  of  simple  ethers 
includes  the  chlorides,  bromides,  iodides,  sulphides,  etc.  of  the 
radicals,  and  in  general  those  compounds  which  correspond  to  the 
simple  salts  of  the  metals,  —  that  is,  those  salts  formed  by  an  acid 
containing  no  oxygen. 

These  compounds  may  be  made  by  heating  together  the  corre- 
sponding acid  and  alcohol.  If  methyl  alcohol  is  heated  with 
strong  hydrochloric  acid,  a  colorless  gas,  methyl  chloride,  CH3C1, 
is  disengaged. 

317.  ETHYL  IODIDE,  C2H5L  —  In  a  glass  flask  we  put  some 
alcohol  with  about  two-thirds  its  weight  of  amorphous  phospho- 
rus ;  to  this  flask  we  fit  a  cork,  through  which  passes  a  bottle- 
shaped   tube  called  an  adapter.      We  have  partially  closed  the 
lower  end  of  the  adapter  with  some  broken  glass,  and  on  this  have 
placed  a  mixture  of  broken  glass  with  a  quantity  of  iodine  equal 
to  two  and  three-fourths  times  the  weight  of  the  alcohol.     The 


ETHYL    IODIDE    AND    BROMIDE. 


205 


upper  end  of  the  adapter  is  connected  with  a  condenser  so  inclined 
thai  liquid  may  flow  from  it  into  the  flask  (Fig.  94).     When  we 

heat  the  flask, 
the  alcohol 
boils,  and  its 
vapor,  conden- 
sing, runs  back 

through  the  iodine,  which  is  dissolved  and 
brought  gradually  in  contact  with  the  amor- 
phous phosphorus.  Phosphorus  tri-iodide, 
PI3,  is  then  formed ;  but  this  immediately 
reacts  with  the  alcohol,  forming  ethyl  iodide 
and  phosphorous  acid.  The  whole  reaction 
is  expressed  in  the  equation 

3C2IROH  +  P  +  I3  =  3C2H5I     +     P(OH)3 
Alcohol.  Ethyl  iodide.   Phosphorous  acid. 

When  the  reaction  has  terminated,  we 
agitate  the  contents  of  the  flask  with  a  dilute 
solution  of  sodium  hydrate,  and  decant  the 
aqueous  liquid  from  the  heavy  oily  layer  of 
ethyl  iodide.  We  then  remove  all  traces  of 
water  from  the  latter  by  shaking  it  with 
some  fragments  of  calcium  chloride,  and  may 
further  purify  it  by  fractional  distillation. 

Ethyl  iodide  is  a  colorless  liquid,  having 
at  0°  a  density  of  1.975.     It  boils  at  72°. 

:)>18.  ETHYL  BROMIDE,  C2H5Br,  may  be  made  by  distilling  a 
mixture  of  alcohol,  potassium  bromide,  and  sulphuric  acid  diluted 
with  its  weight  of  water,  the  substances  being  used  in  the  pro- 
portions required  by  the  equation 

C2H5.0H     -j-     KBr     +     H2SO*     =     C2H5Br     +     KHSO*     +     H20 
It  is  a  liquid  having  a  pleasant  odor,  and  boiling  at  40°.     It  is 
sometimes  used  as  an  anaesthetic. 

319.  By  various  means  the  hydrogen  atoms  of  these  simple  ethers  may  be 
replaced  by  chlorine,  bromine,  or  iodine,  and  compounds  are  then  formed 
wh.eh  we  may  consider  as  derived  from  other  radicals.  By  the  replacement 

18 


FlG.  94. 


206  LESSONS    IN   CHEMISTRY. 

of  a  hydrogen  atom  in  ethyl  bromide  by  a  bromine  atom,  we  may  obtain 
either  ethylene  bromide,  CH2Br-CH2Br,  or  an  isomeric  compound  called 
ethylidene  bromide,  CH3-CHBr2.  One  of  the  more  important  of  the  sub- 
stances derived  by  the  continued  replacement  of  the  hydrogen  atoms  of  a 
simple  ether,  is  chloroform. 

320.  CHLOROFORM,  CHOP,  may  be  made  by  passing  methyl 
chloride  mixed  with  chlorine  over  charcoal  heated  to  about  200°. 
It  is  usually  manufactured  by  distilling  a  mixture  of  alcohol  and 
chlorinated  lime,  commonly  called  bleaching  powder.  The  reaction 
is  very  complex.  Chloroform  and  water  condense  together  in  the 
receiver,  and  the  chloroform  separates  in  a  heavy  oily  layer,  for  it 
is  hardly  soluble  in  water.  It  is  decanted,  shaken  first  with  water 
and  then  with  a  solution  of  potassium  carbonate  to  remove  im- 
purities, and  then  distilled  with  calcium  chloride,  which  removes 
the  little  water  which  it  held  in  solution. 

Chloroform  is  a  colorless  liquid  having  a  pleasant,  stimulating 
odor,  and  a  sweet,  burning  taste.  Its  density  is  1.5,  and  it  boils 
at  60.8.  It  is  not  inflammable,  and  communicates  a  green  tint 
to  a  flame  in  which  a  drop  of  it  is  introduced  on  the  end  of  a 
glass  rod.  It  is  used  as  an  anaesthetic. 

321.  There  is  a  bromoform,  CHBr3,  a  heavy,  colorless  liquid,  and  iodoform, 
CHI3,  a  yellow,  crystalline  solid.  They  are  formed  by  the  action  of  bromine 
and  iodine  on  alcohol  in  presence  of  alkaline  hydrates  or  carbonates. 


LESSON    XL. 

ALDEHYDES,  CARBON  ACIDS,  AND  COMPOUND 
ETHERS. 

322.  In  a  small  beaker,  we  mix  some  ordinary  alcohol  with  a 
little  potassium  dichromate  and  some  strong  sulphuric  acid.  The 
mixture  becomes  warm,  and  the  red  color  of  the  potassium  dichro- 
mate is  changed  to  green.  Potassium  dichromate,  a  compound 
derived  from  chromic  acid,  contains  much  oxygen,  and  it  is  re- 
duced by  the  alcohol,  which  becomes  oxidized.  The  peculiar  odor, 
somewhat  resembling  that  of  apples,  which  is  developed  in  the 


ALDEHYDE. — CHLORAL.  207 

be;  ker  glass,  is  due  principally  to  a  substance  called  aldehyde. 
Its  composition  is  C2H40,  and  it  represents  alcohol  in  which  the 
hy<lroxyl  and  one  hydrogen  atom  are  replaced  by  an  atom  of  oxy- 
gen. 

CH3-CH2.0H     +     0         =         CH3-CHO     +     H'O 
Alcohol.  Aldehyde. 

.ildehyde  is  made  by  distilling  a  mixture  of  alcohol,  sulphuric 
aci  1,  and  potassium  dichromate,  and  condensing  the  product  in  a 
rec  eiver  surrounded  by  ice.  It  is  a  very  volatile  liquid,  boiling 
at  21°. 

>23.  To  aldehyde  correspond  compounds  of  the  same  nature 
de  ived  from  each  primary  alcohol.  In  each  of  them  the  hydroxyl 
an  I  one  atom  of  hydrogen  of  the  corresponding  alcohol  are  re- 
pi;  3ed  by  an  atom  of  oxygen. 

$24.  There  is  an  interesting  derivative  of  aldehyde  produced 
by  the  prolonged  action  of  chlorine  on  absolute  alcohol.  _  It  is  an 
oil  r  liquid,  called  chloral,  and  represents  aldehyde  in  which  three 
hy  Irogen  atoms  are  replaced  by  three  atoms  of  chlorine. 

CCIMJHO  CH3-CHO 

Chloral.  Aldehyde. 

Chloral,  or  trichloraldehyde,  combines  directly  with  water,  form- 
ini  a  crystalline  compound  called  chloral  hydrate.  This  is  much 
use  d  in  medicine  for  its  sleep-producing  properties. 

525.  We  may  consider  that  an  aldehyde  is  an  oxidation  product 
of  m  alcohol.  If  the  oxidation  proceed  still  further,  the  aldehyde 
is  in  its  turn  converted  into  an  acid,  and  the  conversion  of  an 
alcohol  into  an  acid  may  take  place  without  the  previous  forma- 
tion of  an  aldehyde. 

Indeed,  a  carbon  acid  may  be  considered  as  a  primary  alcohol 
in  which  the  hydroxyl  remains,  but  the  two  atoms  of  hydrogen 
related  to  the  same  carbon  atom  as  the  hydroxyl  are  replaced  by 
an  atom  of  oxygen. 

CH3-CH2.OH     +     O2     =     CH3-CO.fcH     +     R2Q 
Alcohol.  Acetic  acid. 

We  consider,  then,  that  a  carbon  acid  is  a  compound  contain- 
ing the  monatomic  group  of  atoms  CO. OH,  and  this  group  is 
ofton  called  carloxyL  As  in  all  acids,  the  hydrogen  of  the  hy- 


208  LESSONS    IN    CHEMISTRY. 

droxyl  group  may  be  replaced  by  metal,  and  salts  are  so  formed. 
If  there  be  only  one  carboxyl  group  in  the  acid,  there  can  be  only 
one  series  of  salts ;  but  if  there  be  two  carboxyl  groups,  we  can 
understand  that  either  both  or  only  one  of  the  hydrogen  atoms 
may  be  replaced,  and  there  will  be  two  series  of  salts,  neutral 
salts  and  acid  salts. 

326.  Formic  Acid,  HCO.OII,  is  the  acid  formed  by  the  oxi- 
dation of  methyl  alcohol.     We  have  already  seen  that  it  may  also 
be  produced  from  hydrocyanic  acid.     It  exists  naturally  in  certain 
insects,  and  it  takes  its  name  from  its  existence  in  ants.     It  is 
made  by  distilling  oxalic  acid  with  glycerin,  taking  care  that  the 
temperature  of  the  mixture  does  not  rise  above  100°.    The  oxalic 
acid  then  forms  with  the  glycerin  a  compound  which  is  again  de- 
composed by  the  heat,  and  dilute  formic  acid  distils,  while  the 
glycerin  is  regenerated. 

C2Q*H2        =        HCO.OH        +        CO2 
Oxalic  acid.  Formic  acid. 

Formic  acid  is  a  colorless,  very  acid  liquid,  having  a  pungent 
odor.  It  freezes  at  8.5°,  and  boils  at  99°.  It  mixes  with  water 
in  all  proportions.  To  a  little  formic  acid  in  a  test-tube,  we  add 
some  strong  sulphuric  acid,  and  gently  heat  the  tube :  an  effer- 
vescence takes  place,  and  we  may  light  the  escaping  gas  at  the 
mouth  of  the  tube.  It  is  carbon  monoxide,  for  the  formic  acid 
has  been  decomposed  into  that  gas  and  water. 

HCO.OH    =    CO     +    H20 

By  replacement  of  the  hydrogen  of  the  hydroxyl  in  formic  acid, 
formates  are  produced:  they  are  soluble  in  water,  and  yield  carbon 
monoxide  when  heated  with  sulphuric  acid. 

327.  Acetic  Acid,   C2H402  r=  CH3-CO.OH,  is  obtained  in 
large  quantities  during  the  manufacture  of  charcoal  by  the  distilla- 
tion of  wood  in  close^  vessels  (§  226).     The  liquids  which  con- 
dense in  this  operation  consist  of  tarry  matter,  dilute  acetic  acid, 
wood-spirit,  and  some  other  substances.     After  the  tar  has  been 
separated,  the  acid  liquid  is  neutralized  with  lime,  and  a  crude 
calcium  acetate,  generally  called  pyrolignite  of  lime,  is  so  formed. 


ACETIC    ACID. 


209 


Tl  is  is  mixed  with  sodium  sulphate,  and  the  sodium  acetate  and 
in.-oluble  calcium  sulphate  formed  are  separated  by  filtration. 
Ca(C2H302)2         +         Na2SO*        =         CaSO4         + 


Calcium  acetate. 


Sodium  acetate. 


The  sodium  acetate  is  then  purified  by  crystallization,  and,  by 
hi  ating  it  with  strong  sulphuric  acid,  is  again  converted  into 
so  lium  sulphate  and  acetic  acid  which  distils. 

328.  Vinegar  is  a  dilute  acetic  acid  produced  by  the  oxidation 
ol  alcohol.     The  oxidation  is  brought  about  by  a  minute  organ- 
iz<  d  ferment  which  has  the  property  of  absorbing  oxygen  from  the 
ai  •  and   transferring  it  to  the  alcohol.     The  change  is  called  the 
ac  >tic  fermentation  :  it  does  not  take  place  in  strong  alcohol.     In 
01  e  method  of  manufacture, 

tl  3  dilute  alcohol,  or  wine,  is 
al  owed  to  trickle  over  beech- 
w  »od  shavings  contained  in 
a  arge  cask  having  a  double 
bi  ttom  and  numerous  perfo- 
rm ;ions  for  the  circulation  of 
ai  •  (Fig.  95).  A  large  num- 
bc  r  of  these  casks  are  placed 
in  rows,  and  the  shavings  are 
first  saturated  with  some  beet- 
jiace  or  sour  wine  in  which 
th  3  ferment  is  already  devel-  ^ 
oped.  The  slow  oxidation  Jj 
of  the  alcohol  produces  so 
much  heat  that  the  temper-  FIG.  95. 

ature  rises  to  30°.       It  is 

usually  necessary  to  allow  the  same  liquid  to  pass  twice  through 
the  cask  before  all  of  the  alcohol  is  changed  to  vinegar. 

329.  Pure  acetic  acid  is  a  corrosive  liquid,  having  a  pungent 
odor.     Its  density  at  0°  is  1.08;  it  freezes  at  17°,  and  boils  at 
118°.     It  is  soluble  in  all  proportions  of  water  and  alcohol. 

In  a  test-tube  we  neutralize  a  few  drops  of  acetic  acid  with  a 
fragment  of  solid  potassium  hydrate :    then  we  introduce  a  few 
o  18* 


210  LESSONS    IN    CHEMISTRY. 

grains  of  arsenious  oxide,  and  heat  the  tube.  Dense  white  vapors, 
having  a  very  unpleasant  garlicky  odor,  are  disengaged.  These 
are  due  to  the  formation  of  a  very  poisonous  compound  called 
cacodyl.  The  test  enables  us  to  recognize  an  acetate. 

330.  Acetates. — Acetic  acid  contains  only  one  atom  of  hydrogen  capable 
of  replacement  by  metal,  and  the  acetates  must  contain  one  atom  of  a  metal 
united  with  one  or  more  groups,  C2H302,  according  to  the  atomicity  of  the 
metal. 

331.  SODIUM  ACETATE,  NaC2H302,  crystallizes  in  large  colorless  prisms  con- 
taining three  molecules  of  water.     The  crystals  effloresce  in  dry  air,  and  the 
water  may  be  entirely  driven  out  by  heat.     It  is  very  soluble  in  water. 

332.  LEAD  ACETATE,  Pb(C2H302)2,  is  commonly  called  sugar  of  lead.     Its 
crystals  also  contain  three  molecules  of  water,  and  have  a  sweet  taste.     It  is 
made  by  dissolving  lead  oxide,  PbO,  in  acetic  acid.     Solutions  of  lead  acetate 
are  capable  of  dissolving  an  excess  of  lead  oxide,  and  when  carbon  dioxide 
is  passed  through  the  liquid,  lead  carbonate  is  precipitated,  while  the  neutral 
acetate  remains  in  solution.     Lead  acetate  is  poisonous. 

333.  COPPER  ACETATE,  Cu(C2Ha02)2  +  H20,  forms  beautiful  bluish-green 
crystals.     Verdigris  is  a  combination  of  copper  acetate  and  cupric  oxide,  CuO. 

334.  Before  leaving  acetic  acid,  we  must  study  one  interesting  manner  of  its 
formation.     We  know  that  hydrochloric  acid  or  an  alkaline  hydrate  will  con- 
vert hydrocyanic  acid  into  formic  acid  or  an  alkaline  formate  (§  263).    If  the 
hydrogen  of  hydrocyanic  acid  be  replaced  by  a  methyl  group,  CH3,  methyl 
cyanide  is  obtained,  CH3.CN  :  when  this  methyl  cyanide  is  boiled  with  potassium 
hydrate,  ammonia  is  disengaged,   and  the  solution  contains  potassium  acetate. 

CH3.CN        +         KOH     +     H20    -     NH3         +       CH3.CO.OK 
Methyl  cyanide.  Potassium  acetate. 

Since  we  have  found  such  strong  reasons  for  believing  that  the  two  carbon 
atoms  of  acetic  acid  are  combined  together,  we  must  believe  that  the  two  carbon 
atoms  in  methyl  cyanide  are  so  combined;  in  hydrocyanic  acid  the  hydrogen 
atom  which  occupies  the  same  relation  as  the  carbon  of  the  methyl  group  in 
methyl  cyanide  must  then  also  be  combined  directly  with  the  carbon. 

This  conversion  of  methyl  cyanide  into  acetic  acid  is  only  an  example  of  a 
general  reaction  of  the  cyanides  of  carbon  radicals  ;  by  boiling  with  potas- 
sium hydrate,  the  nitrogen  atom  is  always  changed  for  an  atom  of  oxygen  and 
the  group  OK,  thus  forming  a  salt  of  that  carbon  acid  which  contains  one  more 
carbon  atom  than  the  radical  of  the  cyanide. 

335.  The  general  formula  of  the  series  of  acids  derived  from  the  monatoniic 
alcohols  is  CnH2n02.    The  higher  members  of  this  series  form  part  of  the  natural 
fats,  and  the  series  is  generally  called  the  series  of  fatty  acids.  The  third  acid 
is  propionic  acid,  C3H602.    There  are  two  butyric  acids  :  one  of  them  exists  in 
butter,  and  the  other  may  be  obtained  by  the  action  of  potassium  hydrate  on 
isopropyl  cyanide.     There  are  three  valeric  acids,  C5111002;  the  most  com- 


COMPOUND    ETHERS. 


211 


mon  exists  naturally  in  valerian  root  and  angelica  root.  It  is  a  colorless  liquid, 
having  a  strong  and  unpleasant  odor. 

;  36.  Compound  Ethers. — In  a  glass  flask  connected  with  a 
gool  condenser  (Fig.  96)  we  distil  a  mixture  of  strong  alcohol 


FIG.  96. 


wit  li  nearly  twice  its  weight  of  strong  sulphuric  acid  and  three 
tines  its  weight  of  crystallized  sodium  acetate.  A  colorless, 
vol  itile  liquid,  having  a  fragrant  odor,  condenses  in  the  receiver. 
Th  s  body  is  ethyl  acetate,  and  has  been  formed  by  the  replace- 
me  it  of  the  sodium  atom  in  sodium  acetate  by  an  ethyl  group. 

NaC2H302    +    C2H5.OH    +   IPSO4   =   C2H5.C2H302   +   NaHSO4   +    H20 
^  iclium  acetate.  Ethyl  acetate. 

Ethyl  acetate  is  a  compound  ether  ;  the  compound  ethers  are 
formed  by  the  replacement  of  the  basic  hydrogen  in  any  oxygen 
acid  by  a  hydrocarbon  radical.  They  are  the  salts  of  the  hydro- 
carbon radicals,  just  as  sodium  acetate  is  a  salt  of  sodium.  Their 
corresponding  acids  may  be  carbon  acids  or  some  of  the  other  acids 
which  we  have  already  studied:  they  may  be  formed  and  decom- 
posed by  double  decomposition,  like  the  salts  of  the  metals.  We 
mix  a  little  ethyl  iodide  with  an  alcoholic  solution  of  silver 
nitrate ;  a  yellow  precipitate  of  silver  iodide  is  formed,  and  the 
liquid  contains  ethyl  nitrate. 

C2H5I  +  AgNO3  Ag  I  +         C2H5.N03 

Ethyl  iodide.  Silver  nitrate.  Silver  iodide.  Ethyl  nitrate. 


212  LESSONS   IN   CHEMISTRY. 

We  gently  heat  some  ethyl  acetate  with  an  alcoholic  solution  of 
potassium  hydrate  ;  the  odor  of  the  ethyl  acetate  disappears ;  po- 
tassium acetate  and  alcohol  have  been  formed. 

C2H5.C2H302     +     KOH     =     KC2H302     -f     C2H5.0H 

We  see  by  these  reactions  that  the  compound  ethers  are  pre- 
cisely analogous  to  the  metallic  salts. 

337.  These  ethers  are  odorous  substances,  and  many  of  those 
in  which  both  basic  and  acid  radical  are  carbon  compounds,  exist 
naturally  in  fruits,  of  which  the  odors  are  due  to  the  ethers. 
Ethyl  formate,  C2H5.CH02,  exists  in  rum  ;  ethyl  valerate  and 
amyl  acetate  probably  exist  in  pineapples  and  bananas.  These 
ethers  may  be  prepared  artificially  by  processes  analogous  to  that 
described  for  ethyl  acetate,  or  they  may  be  made  by  passing  hydro- 
chloric acid  gas  through  a  mixture  of  the  corresponding  acid  and 
alcohol.  In  this  case  water  and  a  simple  ether  (chloride)  are  first 
formed,  and  the  latter  at  once  reacts  with  the  carbon  acid,  the 
result  being  a  compound  ether,  while  hydrochloric  acid  is  regen- 
erated. 


LESSON    XL  I. 
CARBON  ACIDS  AND  COMPOUND  ETHERS   (2). 

338.  Fatty  Acids. — As  the   number  of  carbon  atoms  in  the 
fatty  acids  increases,  these  substances  are  more  oily  in  nature  and 
more  insoluble  in  water.     They  are  liquids  at  ordinary  tempera- 
tures until  the  molecule  contains  nine  atoms  of  carbon,  C9H1802 ; 
the  others  are  solids,  and  the  melting  point  is  higher  as  the  com- 
position is  more  complex.     Compound  ethers  of  these  acids  exist 
in  various  vegetable   products   and   in   animal  secretions.      The 
peculiar  odors  of  animals  are  due  to  fatty  acid  ethers.     We  must 
pass  by  the  intermediate  members  of  the  series  and  study  more 
particularly  those  which  are  most  largely  used  in  the  arts. 

339.  PALMITIC  ACID,  C16H3202,  exists  in  palm  oil,  where  the 
radical  of  the  acid  is  combined  with  the  radical  C3H5  of  glycerin. 


FATS   AND   OILS.  213 

It  is  manufactured  by  distilling  palm  oil  in  a  current  of  super- 
hea  ed  steam  :  glycerin  and  palmitic  acid  are  formed,  and  the 
latter  solidifies  to  a  white  mass  on  cooling.  This  mass  is  strongly 
pressed,  to  remove  a  liquid  acid,  oleic  acid,  which,  existing  also  in 
a  glycerin  compound  in  the  palm  oil,  is  formed  at  the  same  time. 
Tht  palmitic  acid  is  then  used  for  the  manufacture  of  soap  and 
can  lies. 

:  40.  MARGARIC  ACID,  C17H3402,  exists  in  nearly  all  solid  fats, 
ami  in  olive  oil.  It  forms  white,  crystalline  scales,  fusible  at  60°. 

:  41.  STEARIC  ACID,  C18H3602,  forms  a  large  proportion  of  tal- 
low and  may  be  made  by  decomposing  that  substance  by  super- 
hea  ed  steam.  It  is  a  white  solid,  fusible  at  69°.  It  dissolves  in 
alec  liol  and  ether,  and  may  be  crystallized  from  its  solutions. 
Wi  h  the  exception  of  the  stearates  of  potassium,  sodium,  and 
ami  ionium,  the  salts  of  stearic  acid  are  insoluble  in  water. 

;  42.  Oleic  Acid,  C18H3402.— Olive  oil  contains  the  glycerin 
con  pound  of  an  acid  which  does  not  belong  to  the  series  of  fatty 
acic  s.  It  is  an  unsaturated  carbon  compound,  and  its  molecule 
con  ains  two  atoms  of  hydrogen  less  than  that  of  stearic  acid.  It 
is  c  illed  oleic  acid,  and  exists  in  many  oils  and  fats,  but  always 
mixed  with  certain  of  the  fatty  acid  compounds.  It  is  an  oily 
liquid,  which  freezes  at  4°. 

343.  Fats  and  Oils. — The  natural  fats  and  fatty  oils  are  com- 
pou  id  ethers  in  which  a  glycerin  radical  replaces  the  basic  hydro- 
gen of  the  fatty  acids.     We  have  already  seen  that  glycerin  is  a 
triar,omic  alcohol :  it  contains  three  hydroxyl  groups,  and  in  the 
fats  and  oils  each  hydroxyl  group  is  replaced  by  a  fatty  acid  less 
the  hydrogen  of  its  hydroxyl.     The  natural  fats  must,  then,  repre- 
sent  three  molecules  of  fatty  acid   and  a  molecule  of  glycerin. 
The  names  of  these  fatty  bodies  are  derived  from  those  of  the 
fatty  acids  which  take  part  in  their  formation. 

344.  PALMITIN,  C3H5(CU6H3102)3,  may  be  extracted  from  palm 
oil  which    has    been    solidified   by  cold    and    then    subjected    to 
pressure  to  remove  the  liquid  fatty  matters.     It  is  a  white  solid, 
melting  at  60°. 

345.  MARGARIN,    C3H5(C17H3302/,    and    STEARIN,     C3H5- 


214  LESSONS    IN    CHEMISTRY. 

(C18H3502)3,  are  also  solids ;  they  exist  in  the  solid  fats,  such  as 
tallow. 

346.  OLEIN,  C3H5(C18H3302)3,  constitutes  the  greater  portion 
of  olive  oil,  almond  oil,  and  other  analogous  oils.     It  is  a  liquid, 
which  solidifies  at  10°. 

Oils  are  usually  classed  as  fat  oils  and  drying  oils.  The  first 
are  such  as  do  not  solidify  on  exposure  to  air,  but  become  rancid 
and  acquire  an  unpleasant  odor.  They  are  numerous,  and  include 
olive  oil,  cotton-seed  oil,  oil  of  sweet  almonds,  peanut  oil,  and 
many  others.  The  drying  oils,  of  which  the  type  is  linseed  oil, 
absorb  oxygen  and  become  thick  and  hard  when  exposed  to  the 
air ;  they  are  used  in  the  preparation  of  paints  and  varnishes. 

347.  Saponification. — The     decomposition     of    a    compound 
ether  by    a  metallic  hydrate,  a  decomposition  which  results  in 
the  formation   of   a  metallic  salt  and  an  alcohol,  is  in  chemical 
language  called  saponification  ;  however,  a  more  restricted  sense 
of  the  word  implies  the  decomposition  of  a  fatty  body,  with  the 
formation  of  soap  and  glycerin.     We  boil  some  palm  oil  or  olive 
oil  with  a  solution  of  sodium  hydrate ;  the  oil  disappears,  and  a 
soap  has  been  formed,  while  glycerin  is  set  free  in  the  liquid.     It 
is  necessary  that  ordinary  soaps  shall  be  soluble  in  water,  and  we 
have  already  seen  that  the  only  ordinary  metals  which  yield  solu- 
ble salts  with  the  fatty  acids  are  potassium  and  sodium  ;  in  other 
words,  the  alkaline  metals  (§  341).    Soap,  then,  is  an  alkaline  salt 
of  one  of  the  higher  fatty  acids,  generally  palmitic,  stearic,  and 
margaric  acids,  to  which  must  be  added  oleic  acid.     Soft  soaps 
are  made  with  potassium  hydrate,  while  sodium  hydrate  yields  the 
hard  soaps. 

In  the  manufacture  of  soap,  the  fat  or  oil  is  first  boiled  with  a 
rather  weak  solution  of  sodium  hydrate,  generally  known  as  con- 
centrated lye,  and,  when  the  mixture  becomes  pasty,  enough  strong 
sodium  hydrate  is  added  to  saponify  the  fat  completely.  To  sep- 
arate the  excess  of  water,  common  salt  is  added ;  this  dissolves  in 
the  water,  causing  the  soap  to  come  to  the  surface,  for  common 
soap  is  insoluble  in  salt  water.  The  salty  water,  containing  the 
excess  of  alkaline  hydrate  employed,  is  then  drawn  off,  and  the  soap 


SAPONIFICATION.  215 

hare  ens  on  cooling.  As  it  is  not  easy  to  separate  from  the  waste 
liqu  d  the  glycerin  formed  in  the  reaction,  it  is  more  economical  to 
dec*  rapose  the  fat  by  superheated  steam,  and  boil  with  sodium  hy- 
drat3  the  fatty  acid  which  floats  on  the  dilute  glycerin.  While 
soaj  is  soluble  in  water,  it  is  decomposed  by  a  large  quantity  of  that 
liqu  d,  a  small  quantity  of  alkaline  hydrate  being  set  free,  while 
the  fatty  acid  becomes  insoluble.  The  free  alkali  produces  the 
clea  ising  effects,  and  the  fatty  acid  forms  the  lather  :  we  know 
thai  soap  will  not  produce  a  lather  if  we  use  too  little  water. 
Ord  nary  soap  is  insoluble  in  salt  water,  but  a  soap  which  is  sol- 
ublt  in  salt  water  may  be  made  from  cocoanut  oil  ;  it  is  called  salt- 
wat<  r  soap.  It  contains  an  alkaline  laurate  and  myristate,  lauric 
aci<  ,  C12H2402,  and  myristic  acid,  C14H2802,  existing  as  glycerin 
ethi  rs  in  cocoanut  oil. 

3  18.  STEARIN  CANDLES  are  made  from  a  mixture  of  solid 
fatt  acids  obtained  by  saponifying  tallow  by  superheated  steam 
and  a  small  quantity  of  lime.  The  small  quantity  of  insoluble 
calc  um  soap  so  formed  is  decomposed  by  sulphuric  acid,  and  the 
olei<  acid  is  separated  from  the  solid  acids  by  pressing  the  mass 
betveen  warm  plates.  The  oleic  acid  is  used  for  the  manufacture 
of  s  )ap.  Certain  fatty  bodies,  among  them  palm  oil,  are  entirely 
decomposed  by  superheated  steam,  without  the  aid  of  lime.  In 
this  reaction  the  water  acts  as  would  either  an  acid  or  an  alkaline 
hyd  'ate,  part  of  its  molecule  completing  the  basic  molecule  of 
glyc?rin,  while  the  other  part  completes  the  acid  molecule. 


+     3HOH     =     C3H5(OH)3     +     3C16I13202 
Palmitin.  Glycerin.  Palmitic  acid. 

The  saponification  of  fats  and  oils  may  be  brought  about  by  the 
action  of  strong  acids,  such  as  sulphuric  acid,  for  the  strong  acid 
foms  a  new  compound  ether  with  the  glycerin  radical,  and  sets 
the  fatty  acid  free  ;  the  compound  ether  may  then  be  again 
decomposed  into  glycerin  and  acid  by  the  addition  of  water. 


216  LESSONS    IN   CHEMISTRY. 

LESSON    XLIL 
CARBON  ACIDS   (3). 

349.  Lactic  Acid,  C3H603,  is  a  product  of  the  fermentation 
of  milk,  and  of  a  peculiar  fermentation  which  glucose  undergoes 
in  the  presence  of  basic  substances  which  will  neutralize  the  acid 
as  fast  as  it  is  formed.     It  is  usually  made  by  allowing  a  solution 
of  glucose  to  which  some  sour  milk,  a  little  old  cheese,  and  some 
chalk  have  been  added,  to  ferment  in  a  warm  place  until  the  whole 
is  converted  into  a  solid  mass  of  calcium  lactate.    This  salt  is  then 
purified  by  crystallization,  and  is  decomposed  by  the  exact  quan- 
tity of  sulphuric  acid  required  to  precipitate  all  of  the  calcium  in 
the  form  of  insoluble  calcium    sulphate.     The  solution  of  lactic 
acid  is  then  separated  by  a  filter,  and  evaporated  on  a  water-bath. 
Lactic  acid  remains  as  a  colorless,  very  sour,  syrupy  liquid,  which 
is  decomposed  when  heated. 

Lactic  acid  is  propionic  acid,  C3H602,  in  which  one  atom  of  hydrogen  is 
replaced  by  a  hydroxyl  group  ;  it  is  consequently  at  the  same  time  an  alcohol 
and  an  acid.  Chemists  have  obtained  another  acid  of  the  same  composition, 
an  isomeride  of  lactic  acid,  and  the  differences  of  the  two  are  due  to  different 
positions  of  the  hydroxyl  group.  The  isomeric  lactic  acid  is  called  hydracrylic 
acid,  because  it  is  decomposed  by  heat  into  water  and  an  acid  called  acrylic 
acid,  C3H402. 

CH3-CH2-CO.OH          CH3-CH(OH)-CO.OH  CH2(OH)-CH2-CO.OH 

Propionic  acid.  Lactic  acid.  Hydracrylic  acid. 

350.  Oxalic  Acid,   C2H204,  exists  naturally  in  many  plants  ; 
it  gives  the   sour  taste  to  sour  grass,  and  at  certain  seasons  is 
present  in  small  quantities  in  rhubarb-leaves.     It  is  a  product  of 
the  oxidation   of  many  vegetable   matters :  it  may  be  made  by 
boiling  starch  with  rather  dilute  nitric  acid,  and  evaporating  the 
liquid.     It  is  now  manufactured  by  heating  to  200°  a  pasty  mix- 
ture of  saw-dust  and  potassium  hydrate ;  potassium  oxalate  is  so 
formed,  and  is  separated  by  treating  the  mass  with  hot  water,  in 
which  it  is  quite  soluble.     The  solution  of  potassium  oxalate  is 


OXALIC   ACID.  217 

then  mixed  with  milk  of  lime,  which  is  calcium  hydrate,  and  in- 
soluble calcium  oxalate  is  formed,  while  the  solution  contains 
pot;  ssium  hydrate,  which  is  used  for  another  operation. 

K2C20*  +  Ca(OH)2  CaC204         +         2KOH 

Pota  sium  oxalate.  Calcium  hydrate.  Calcium  oxalate. 

The  calcium  oxalate  is  decomposed  by  sulphuric  acid,  which 
fori  is  insoluble  calcium  sulphate,  and  the  solution  of  oxalic  acid  is 
eva  torated  until  it  is  strong  enough  to  crystallize. 

( >xalic  acid  forms  large,  colorless  prisms,  containing  two  mole- 
cul  s  of  water  of  crystallization.  In  "dry  air,  these  crystals  efflo- 
res<  e,  and  the  anhydrous  acid  may  be  obtained  by  carefully  heating 
the  11  to  100°.  Oxalic  acid  dissolves  in  fifteen  times  its  weight 
of  i  )ld  water,  and  is  also  soluble  in  alcohol.  When  heated  to  about 
15(  °,  it  is  decomposed  with  formation  of  carbon  monoxide,  carbon 
dio  :ide,  formic  acid,  and  water. 

2C2H20*  CO        +        2C02         +        CH202        +        IPO 

<   valic  acid.  Formic  acid. 

Ve  have  already  learned  that  both  carbon  monoxide  and  formic 
aci' ;  are  prepared  by  the  decomposition  of  oxalic  acid. 

!  51.  We  neutralize  a  solution  of  oxalic  acid  by  the  addition  of 
a  little  ammonia-water,  and  then  pour  into  it  some  solution  of 
calcium  chloride.  A  white  precipitate  of  insoluble  calcium  oxalate 
is  fcrmed. 

(>H*)2C20*         +  CaCl2  2NH*C1  -f         CaC20* 

Amu  oniuni  oxalate.        Calcium  chloride.         Ammonium  chloride.       Calcium  oxalate. 

Oxalic  acid  is  poisonous;  its  antidote  is  chalk,  which  is  calcium 
carl'onate:  this  causes  the  formation  of  insoluble  calcium  oxalate. 

We  have  prepared  some  silver  oxalate  by  adding  solution  of 
silver  nitrate  to  a  solution  of  oxalic  acid  neutralized  with  ammonia. 
The  insoluble  silver  oxalate  is  separated  by  nitration  and  dried. 
When  we  heat  a  small  quantity  of  this  powder  in  a  test-tube,  it 
suddenly  explodes,  being  decomposed  into  carbon  monoxide,  carbon 
dioxide,  and  silver. 

Since  oxalic  acid  contains  two  carboxyl  groups,  CO. OH,  it  is  a  dibasic  acid; 

it  contains  two  atoms  of  replaceable  hydrogen,  and  with  monatomic  metals 

may  form  two  scries  of  salts,  acid  oxalates,  in  which  only  one  atom  of  hydrogen 

is  replaced  by  metal,  and  neutral  salts,  in  which  both  atoms  are  so  replaced. 

K  19 


218  LESSONS    IN   CHEMISTRY. 

One  atom  of  a  diatomic  metal  like  calcium  will  of  course  replace  both  hydrogen 
atoms. 

With  the  exception  of  the  oxalates  of  potassium,  sodium,  and  ammonium,  all 
of  the  neutral  oxalates  of  the  ordinary  metals  are  insoluble  in  water,  but 
dissolve  in  dilute  acids  such  as  sulphuric  and  hydrochloric  acids. 

352.  Tartaric  Acid,  C4H606,  is  the  acid  of  grapes.     In  the 
casks  in  which  wine  is  kept,  there  is  deposited  an  impure  potas- 
sium acid  tartrate,  called  argol.    This  is  purified  by  crystallization 
from  boiling  water,  and  the  pure  potassium  acid  tartrate  so  obtained 
constitutes  cream  of  tartar.     By  boiling  the  cream  of  tartar  with 
chalk,  and  adding  -  sufficient  calcium  chloride  to  form  potassium 
chloride  with  the  potassium,  insoluble  calcium  tartrate  is  formed, 
while  carbon  dioxide  is  given  off,  and  potassium  chloride  remains 
in  solution.     The  calcium  tartrate  is  separated  by  filtration,  and, 
after  being  washed  with  water,  is  decomposed  by  the  exact  quantity 
of  dilute  sulphuric  acid.     Calcium  sulphate  is  precipitated,  and 
when  the  filtered  solution  has  been  sufficiently  concentrated  by 
evaporation,  crystals  of  tartaric  acid  are  formed. 

Tartaric  acid  is  in  large,  prismatic  crystals,  soluble  in  about 
half  their  weight  of  cold  water,  and  also  soluble  in  alcohol.  By 
the  action  of  heat  it  is  converted  into  several  other  acids,  of  which 
the  compositions  depend  on  the  temperature  at  which  the  tartaric 
acid  is  decomposed. 

353.  We  can  easily  understand  .the  molecular  constitution  of  tartaric  acid 
by  studying  that  of  substances  to  which  it  is  intimately  related.     When  ethy- 
lene  cyanide  (CN)CH2-CH2(CN)  is  boiled  with  potassium  hydrate,  ammonia 
is  disengaged,  and  there  is  formed  the  potassium  salt  of  succinic  acid,  so  called 
because  it  is  formed  by  the  action  of  heat  on  amber. 

CH2-CN  CH2-CO.OH                   9NT?3 

i  A*WIC\                 i                            '         /rs±iQ 

CH'-CN  CR2-CO.OH 

Ethylene  cyanide.  Succinic  acid. 

There  exists  in  apples,  gooseberries,  and  many  other  fruits  an  acid  called 
malic  acid,  and  this  has  also  been  prepared  artificially  in  such  a  manner  as  to 
show  that  it  represents  succinic  acid  in  which  one  atom  of  hydrogen  is  replaced 
by  a  hydroxyl  group.  The  replacement  of  two  hydrogen  atoms  of  succinic 
acid  by  hydroxyl  groups  yields  tartaric  acid. 

CH2-CO.OH  CH(OH)-CO.OH  CH(OH)-CO.OH 

CIP-CO.OH  CH2-CO.OH  CH(OH)-CO.OH 

Succinic  acid.  Malic  acid.  Tartaric  acid. 


CITRIC    ACID.  219 

Tartaric  acid  is,  then,  a  diatomic  alcohol,  for  it  contains  two  hydroxyl  groups 
related  to  two  carbon  atoms,  and  it  is  a  dibasic  acid,  for  it  contains  two  car- 
boxyl  groups,  CO. OH. 

Of  monatomic  metals  like  potassium  and  sodium  there  are  two  series  of 
tart  rates,  acid  tartrates,  in  which  only  one  atom  of  basic  hydrogen  is  replaced, 
and  neutral  tartrates,  in  which  both  are  replaced. 

.'154.  POTASSIUM  ACID  TARTRATE,  KC4H506,  is  cream  of 
tar  ar,  and  is  made  by  simply  purifying  the  argol  of  wine-casks. 
It  s  almost  insoluble  in  cold  water,  but  dissolves  in  boiling  water. 

rVhen  cream  .of  tartar  is  heated  to  redness,  it  leaves  a  residue 
of  Charcoal  and  pure  potassium  carbonate,  which  may  be  dissolved 
fro  n  the  mass  by  water.  Pure  potassium  carbonate  is  usually 
obi  lined  in  this  manner. 

155.  POTASSIUM  TARTRATE,  K2C4H406,  is  made  by  adding 
potassium  carbonate  to  a  boiling  solution  of  cream  of  tartar  as 
loi  ^  as  carbon  dioxide  is  disengaged.  When  the  concentrated 
sol  ition  cools,  the  salt  separates  in  crystals  which  are  very  soluble 
in  vvater. 

*56.  POTASSIUM  SODIUM  TARTRATE,  KNaC4H406,  is  com- 
m<  iily  called  Eochelle  salt.  It  is  made  by  neutralizing  with  sodium 
carbonate  a  boiling  solution  of  cream  of  tartar.  It  forms  beau- 
tiful, colorless  crystals,  freely  soluble  in  water. 

.'157.  ANTIMONIO- POTASSIUM  TARTRATE,  K(SbO)C4H*06, 
known  as  tartar  emetic,  is  formed  when  antimonous  oxide  is  boiled 
with  cream  of  tartar.  Its  crystals  contain  one  molecule  of  water 
of  crystallization  for  every  two  molecules  of  the  salt,  and  effloresce 
in  <lry  air.  It  is  soluble  in  water,  and  is  poisonous.  When  hy- 
drogen sulphide  is  passed  through  its  solution,  an  orange-colored 
precipitate  of  antimony  sulphide  is  formed. 

358.  Citric  Acid,  C6H807,  exists  in  lemons,  oranges,  currants, 
and  many  other  fruits.  It  is  made  by  allowing  the  juice  of 
lemons  or  sour  oranges  to  stand  until  it  begins  to  ferment,  and 
then  neutralizing  the  boiling  filtered  liquid  with  chalk.  The  in- 
soluble calcium  citrate  formed  is  washed  with  boiling  water,  and 
decomposed  by  dilute  sulphuric  acid  ;  citric  acid  crystallizes  from 
the  solution  separated  from  the  insoluble  calcium  sulphate. 

Citric  acid  forms  large  colorless  crystals,  soluble  in  about  three- 


220  LESSONS    IN    CHEMISTRY. 

fourths  their  weight  of  cold  water,  and  having  a  very  sour  taste. 
It  is  a  tribasic  acid,  containing  three  carboxyl  groups.  Its  cold 
solutions  are  not  precipitated  by  lime-water,  but  become  turbid 
when  the  liquid  is  boiled,  for  calcium  citrate  is  more  soluble  in 
cold  than  in  hot  water.  Magnesium  citrate  is  employed  as  a 
purgative  in  medicine. 


LESSON    XLIII. 
HYDRATES    OF    CARBON, 

359.  Plants  and  vegetables  contain  a  number  of  compounds 
composed  of  carbon,  hydrogen,  and  oxygen,  the  last  two  elements 
being  present  in  exactly  the  proportions  required  for  the  formation 
of  water.  For  that  reason  these  compounds  are  called  carbo- 
hydrates, or  hydrates  of  carbon.  The  compositions  of  these  sub- 
stances are  expressed  by  three  different  formulae,  but  there  are  a 
number  of  isomeric  compounds  for  each  formula.  Of  all  these 
substances  we  can  study  only  the  more  common,  one  or  two  of 
each  series,  and  the  types  of  the  three  series  are 


C6H10Q5 
Starch.  Glucose.  Saccharose. 

360.  Starch  is  found  everywhere  in  the  vegetable  kingdom, 
and  constitutes  the  greater  part  of  all  grains,  and  of  many  tube- 
rose roots  like  the  potato.  It  is  obtained  by  reducing  potatoes  to 
a  pulp,  and  washing  this  pulp  in  a  sieve  through  which  flows  a 
stream  of  water.  The  fibrous  matters,  consisting  of  the  torn  cells 
of  the  potato,  remain  in  the  sieve,  while  the  small  particles  of 
starch  pass  through  and  are  deposited  from  the  water,  which  is 
allowed  to  flow  slowly  down  long  inclined  planes.  From  grains 
the  starch  is  extracted  by  grinding  the  grain  to  flour,  and  knead- 
ing the  flour  in  a  sieve  under  running  water.  The  starch  passes 
through,  as  .before,  while  the  nitrogenized  matter  of  the  grain 
forms  a  soft,  elastic  mass,  called  gluten. 

The  starch  so  obtained  is  simply  separated  from  the  vegetable 


STARCH. 


221 


cell>  in  which  it  was  formed.  It  occurs  as  a  fine  powder,  in  which 
microscopic  examination  reveals  a  peculiar  granular  structure. 
The  size  and  shape  of  these  granules  vary  with  the  source  of  the 
star oh  (Fig.  97)  :  they  are  from  2  to  185  thousandths  of  a  millimetre 
in  diameter.  They  are  formed  of  concentric  layers,  and  their 
structure  becomes  apparent  when  a  little  starch  is  dried  at  100°, 
and  after  moistening  with  a  drop  of  water  containing  a  trace  of 
iodine,  is  examined  by  the  aid  of  a  microscope.  The  granules 


FIG.  98. 

thei   swell,  and,  as  the  exterior  layers  burst,  the  interior  structure 
is  exposed  (Fig.  98). 

S  arch  is  insoluble  in  water  and  alcohol;  but,  when  it  is  rubbed 
will  water  in  a  mortar  with  rough  sides,  a  small  quantity  of  the 
interior  of  the  granules  appears  to  dissolve.  When  it  is  boiled 
with  a  large  quantity  of  water,  the  granules  burst,  and  a  turbid 
liquid  is  obtained  on  cooling;  this  contains  some  soluble  starch, 
and  holds  in  suspension  the  insoluble  starch.  When  heated  with 
water  to  60°  or  70°,  starch  forms  a  gelatinous  mass,  called  starch 
paste.  We  have  already  seen  that  starch  develops  a  blue  color 
with  iodine  ;  and  as  starch  is  the  test  for  iodine,  so  iodine  is  the 
test  for  starch.  It  is  probable  that  the  blue  substance  is  only 
starch  dyed  by  iodine ;  for,  if  dried  and  exposed  to  the  air,  its 
color  gradually  fades  as  the  iodine  volatilizes. 

\Yhile  the  composition  of  starch  is  represented  by  the  formula 
C6H1005,  it  is  probable  that  this  formula  does  not  express  a  mole- 
cule of  starch,  but  that  the  molecule  contains  a  multiple  of 
C6H1005. 

19* 


222  LESSONS    IN   CHEMISTRY. 

Boiling  with  dilute  acids  converts  starch  into  glucose. 

C6H10Q5  +  H2Q  =  C6H1206 

By  the  influence  of  a  peculiar  substance  called  diastase,  which 
is  formed  during  the  germination  of  grain,  starch  is  converted 
into  an  isomeride  of  glucose,  to  which  the  name  maltose  has  been 
given. 

361.  Dextrin. — When  starch  is  heated  to  between  160°  and 
200°,  it  is  changed  into  a  body  which  is  soluble  in  water,  and 
which  is  not  colored  by  iodine.    It  is  a  pale-yellow  powder,  called 
dextrin.     Its  solution  is  gummy,  and  is  used  as  a  mucilage. 

362.  Cellulose  contains  the  same  proportions  of  carbon,  hydro- 
gen, and  oxygen  as  starch.     It  is  the  matter  which  forms  the 
walls  of  young  cells  in  vegetables,  and  is  deposited,  together  with 
other  matters,  in  the  older  cells.     Linen,  cotton,  paper,  and  the 
pith  of  certain  plants  are  almost  pure  cellulose,  which  may  be 
obtained  by  washing  linen  or  cotton  successively  with  dilute  so- 
lution of   potassium  hydrate,  water,   chlorine-water,  acetic  acid, 
alcohol,  ether,  and  water.     The  insoluble  matter  left  after  these 
operations  is  cellulose. 

It  is  a  translucid,  white  solid,  having  a  density  of  about  1.3. 
It  is  not  soluble  in  either  water,  alcohol,  dilute  acids,  or  alkaline 
hydrates.  It  dissolves,  however,  in  the  blue  liquid  obtained  by 
shaking  copper  with  ammonia- water  in  contact  with  the  air.  By 
the  action  of  strong  sulphuric  acid  on  cellulose,  a  gummy  mass  is 
obtained,  which  long  boiling  with  water  converts  into  fermentible 
glucose. 

When  paper  is  soaked  in  a  cold  mixture  of  sulphuric  acid  with 
half  its  volume  of  water,  and  is  then  thoroughly  washed  and  dried, 
it  is  converted  into  a  semi-transparent  substance,  which  is  called 
vegetable  parchment.  This  is  the  substance  generally  used  for 
dialysis  (§  220). 

363.  GUN-COTTON  is  made  by  soaking  cotton  wool  in  a  mixture 
of  about  equal  volumes  of  strong  nitric  and  sulphuric  acids,  and 
washing  the  product  in  running  water  until  the  last  traces  of  acid 
are  removed.     After  drying  in  the  air,  the  substance  has  all  the 


GLUCOSE.  223 

appearances  of  cotton,  but  is  not  as  soft  to  the  touch.  It  is  very 
in  la  mm  able,  and  burns  with  a  flash,  leaving  no  residue. 

In  gun-cotton,  part  of  the  hydrogen  of  the  cellulose  has  been 
replaced  by  monatomic  nitryl  groups,  NO2,  and  the  properties  of 
tli  3  gun-cotton  are  modified  according  to  the  number  of  hydrogen 
atoms  so  replaced.  The  most  explosive  variety  is  called  pyroxy- 
lii  ,  and  is  probably  a  mixture  of  dinitrocellulose  and  trinitrocellu- 
lo,  e. 

C6H10Q5  C6H8(N02)205  C6H?(N02)305 

Cellulose.  Dinitrocellulose.*  Trinitrocellulose. 

A  large  volume  of  gas  is  produced  by  the  explosion,  and  attempts 
h;>vre  been  made  to  substitute  this  variety  of  gun-cotton  for  gun- 
powder. Gun-cotton  is  insoluble  in  water,  alcohol,  and  ether; 
b\  careful  operations  a  variety  may  be  obtained  which  is  quite 
so  uble  in  a  mixture  of  alcohol  and  ether,  and  the  solution  is  em- 
pi  yed,  under  the  name  collodion,  in  photography  and  in  surgery. 
Tl  e  soluble  variety  is  probably  dinitrocellulose. 

364.  Glucose,  C6H1206,  exists  in  many  fruits,  and  when  pres- 
ei)  in  large  quantity  forms  a  white  efflorescence  on  the  surface 
wl  en  the  fruits  are  dried,  as  is  the  case  with  figs  and  raisins.  The 
sol  .d  matter  which  deposits  in  old  honey  is  glucose. 

Grlucose  is  manufactured  by  boiling  starch  with  a  large  quantity 
of  water  containing  about  one-half  per  cent,  of  sulphuric  acid.  The 
starch  is  not  added  until  the  liquid  is  boiling,  and  after  about  half 
an  hour's  cooking  it  is  completely  converted  into  glucose.  The 
sulphuric  acid  is  then  neutralized  with  chalk,  and  after  the  insol- 
uble calcium  sulphate  has  been  separated  by  filtration,  the  solution 
of  zlucose  is  concentrated  until  it  will  solidify  to  a  crystalline  mass 
on  cooling. 

Glucose  forms  small,  rounded,  crystalline  masses,  which  contain 
one  molecule  of  water  of  crystallization  for  each  molecule  of  glu- 
cose. When  cautiously  heated,  it  melts,  and  again  becomes  solid  at 
100°,  all  the  water  of  crystallization  being  then  expelled.  Glu- 
cose dissolves  in  about  its  own  weight  of  cold  water,  and  the  solu- 
tion has  a  sweet  taste.  It  is  much  employed  in  confectionery  and 
syrups,  but  to  produce  the  same  sweetness  in  a  given  quantity  of 


224  LESSONS   IN    CHEMISTRY. 

solution,  the  glucose  must  be  employed  in  three  times  the  quantity 
of  ordinary  sugar  which  would  be  required. 

In  a  test-tube  we  boil  a  mixture  of  sodium  hydrate  solution, 
potassium  and  sodium  tartrate,  and  cupric  sulphate :  this  is  called 
a  cupro-alkaline  solution,  and  is  not  changed  by  heat,  but  when 
we  add  a  little  glucose  to  the  boiling  liquid,  the  color  changes  to 
yellowish  red,  and  on  standing  red  cuprous  oxide  is  deposited. 
The  glucose  has  reduced  the  cupric  solution  :  glucose  then  acts  as 
a  reducing  agent.  The  reduction  may  even  result  in  the  separa- 
tion of  metal.  To  a  solution  of  silver  nitrate  we  add  ammonia- 
water  until  the  precipitate  at  first  formed  is  just  redissolved.  Now 
on  adding  a  little  glucose  and  gently  warming  the  tube  a  brilliant 
mirror  of  silver  is  formed  on  its  walls.  In  these  reactions  the  glu- 
cose is  oxidized  and  converted  into  complex  acids. 

We  already  know  that  glucose  and  maltose  are  by  fermentation 
decomposed  into  carbon  dioxide  and  alcohol. 

365.  Saccharose,  or  Cane-Sugar,  C12H220".— This  com- 
pound, which  is  ordinary  sugar,  is  extracted  principally  from 
sugar-cane,  sugar-maple,  beet-root,  and  sorghum.  Maple-sugar 
flows  from  incisions  made  in  the  bark  of  the  maple.  Sugar-cane, 
beet-root,  or  the  plants  from  which  sugar  is  to  be  extracted,  are 
finely  cut,  and  subjected  to  strong  pressure,  by  which  the  juice  is 
expressed.  The  liquid  is  then  heated  by  steam  in  large  boilers, 
and  milk  of  lime  (calcium  hydrate)  is  added  to  neutralize  the  nat- 
ural acids  of  the  juice  and  form  insoluble  compounds  with  certain 
nitrogenized  principles  which  are  present.  The  syrup  dissolves  a 
considerable  quantity  of  lime,  and  this  is  precipitated  either  by 
a  current  of  carbon  dioxide,  or  by  ammonium  phosphate,  which 
forms  insoluble  calcium  phosphate,  while  ammonia  is  disengaged. 
The  syrup  is  then  heated,  and  filtered  through  a  layer  of  grained 
animal  charcoal,  and  is  afterwards  concentrated  at  as  low  a  temper- 
ature as  possible  by  boiling  in  large  vessels  in  which  a  vacuum  is 
made  by  pumps.  When  it  is  sufficiently  concentrated,  the  syrup 
is  run  into  cooling-pans,  where  it  is  continually  stirred,  so  that  the 
sugar  may  separate  in  small  crystals,  constituting  granulated  sugar. 
This  sugar  is  purified  or  refined  by  being  again  dissolved  and  fil- 


LACTOSE.  225 

tend  through  animal  charcoal,  after  which  the  syrup  must  be 
aga  n  evaporated  and  crystallized.  Loaf-sugar  is  made  by  placing 
the  still  wet  granulated  sugar  in  conical  moulds  having  a  hole  at 
the  point,  which  is  the  lower  portion.  The  moulds  are  heated  to 
abo.it  25°  in  an  oven,  until  the  sugar  has  formed  a  porous  mass, 
from  which  the  syrup  is  drained  by  opening  the  hole  in  the  mould. 
A  little  very  strong  colorless  syrup  is  then  poured  in,  and  as  this 
cry  ,tallizes  it  renders  the  porous  loaf  hard  and  compact.  Granu- 
lati  1  sugar  is  dried  by  rapid  rotation  in  a  cylinder  of  wire  gauze, 
thr  >ugh  which  the  syrup  is  thrown  by  centrifugal  force ;  it  then 
constitutes  soft  sugar.  The  still  moist  sugar  is  dried  and  con- 
vex ed  into  dry  granulated  sugar  by  being  sifted  on  a  revolving 
cylinder  heated  by  steam  and  contained  in  a  large,  partially  open 
dru  n. 

1  >uring  the  manufacture  of  sugar  a  part  of  that  substance  is  by 
the  action  of  the  heat  and  water  converted  into  two  other  sub- 
stai  ces,  glucose,  and  a  body  isomeric  with  it,  named  levulose. 

C12H22QH     +     H2Q     =     C6H1206     +     CMP206 
Saccharose.  Glucose.  Levulose. 

The  mixture  of  these  substances  can  be  crystallized  only  with 
gre;  .t  difficulty,  and  the  uncrystallizable  syrup  constitutes  molasses. 
Tlu  purest  sugar  is  rock-candy,  and  is  obtained  by  stretching 
thnads  through  a  vessel  containing  a  very  concentrated  syrup. 
Tlu  sugar  then  deposits  in  large  crystals  on  the  threads. 

Sugar  is  insoluble  in  ether  and  in  absolute  alcohol.  Its  crystals 
are  anhydrous.  It  melts  at  160°,  and  on  cooling  forms  a  hard, 
amorphous  mass.  At  about  190°  it  is  partially  decomposed, 
yielding  a  brown,  bitter  substance  known  as  caramel.  It  does  not 
reduce  cupro-alkaline  solutions,  but  by  long  boiling  is  converted 
into  glucose,  which  then  effects  the  reduction. 

366.  Lactose  is  a  hard,  not  very  sweet  substance  which  exists 
in  the  milk  of  animals,  and  is  usually  made  by  simply  evaporating 
the  whey  left  in  the  manufacture  of  cheese.  It  has  the  same 
composition  as  saccharose,  but  its  crystals  contain  one  molecule 
of  water  of  crystallization  to  one  of  lactose,  C12H22On  +  H20. 

267.  The  saccharine  substances,  of  which  we  have  considered  only  a  few, 
P 


226  LESSONS    IN   CHEMISTRY. 

rotate  the  plane  of  polarization  of  polarized  light  passed  through  their  solu- 
tions. Glucose,  saccharose,  and  lactose  turn  it  to  the  right ;  levulose  rotates 
it  to  the  left. 

368.  The  gums  and  mucilages  which  are  obtained  from  certain  plants  are 
analogous  to  saccharose  in  composition.  Gum-arabic,  which  flows  naturally 
from  several  species  of  acacia,  is  said  to  contain  a  body,  arabin,  having  the 
composition  C12H22On. 


LESSON    XLIV. 

BENZOL   DERIVATIVES  (i). 

369.  We  have  already  seen  that  the  unsaturated  hydrocarbon 
benzol,  C6H6,  acts  precisely  like  the  saturated  hydrocarbons,  in  that 
its  compounds  are  formed  by  the  replacement  of  its  hydrogen 
atoms  by  other  atoms  or  groups.     We  have  learned  that  mono- 
chlorobenzol,  C6H6C1,  is  formed  in  this  manner  by  the  replacement 
of  an  atom  of  hydrogen  by  one  of  chlorine.     Since  we  may  con- 
sider that  the  alcohols  are  formed  by  the  replacement  of  one  or 
more  hydrogen  atoms  in  the  saturated  hydrocarbons  by  the  same 
number  of   hydroxyl  groups,  we  can  understand  that  a  similar 
replacement  in  benzol  should  yield  substances  analogous  to  the  al- 
cohols.    While  these  substances  do  resemble  the  alcohols  in  many 
of  their  chemical  relations,  they  have  at  the  same  time  certain 
other  properties ;  the  hydrogen  of  their  hydroxyl  is  more  readily 
replaced  by  atoms  of  metal  than  is  that  of  the  alcohols.     They 
are  called  phenols  ;  the  most  simple  is  that  in  which  only  one 
hydrogen  atom  is  replaced  by  hydroxyl,  and  it  is  ordinary  phenol, 
commonly  called  carbolic  acid. 

370.  Phenol,  C6H5.OH.— This  important  compound  can    be 
prepared  artificially  from  benzol,  but  it  is  always  obtained  from 
coal-tar,  for  it  is  one  of  the  products  of  the  destructive  distillation 
of  coal.     After  the  benzol  has  been  separated  from  the  tar,  that 
portion  which  distils  during  the  fractional   distillation   between 
150°  and  200°  is  collected  separately,  and  is  mixed  with  a  satu- 
rated solution  of  sodium  hydrate.     A  compound  in  which  the 


TRINITROPHENOL.  227 

hydrogen  of  the  hydroxyl  in  phenol  is  replaced  by  sodium  is  so 
formed ;  this  is  dissolved  in  boiling  water,  and  the  solution  sep- 
anred  from  the  oily  matters,  which  remain  unaffected.  The  solu- 
tion of  sodium  phenate  is  then  treated  with  hydrochloric  acid,  the 
rea  -tion  yielding  phenol  and  sodium  chloride. 

C6H5.ONa         +        HC1        =         C6H5.0H         +         NaCl 
Sodium  phenate.  Phenol. 

The  phenol  is  not  very  soluble  in  water,  and  when  it  has  sep- 
ara  ed  is  dried  with  calcium  chloridej  and  distilled.  The  product 
is  t  hen  cooled  in  a  mixture  of  ice  and  salt,  and  the  phenol  forms 
cr}  stals  which  are  separated  and  drained. 

Phenol  crystallizes  in  colorless  needles,  fusible  at  35°  ;  it  boils 
at  86°.  It  has  a  peculiar  characteristic  odor,  and  a  burning 
tas  e.  It  is  only  slightly  soluble  in  water.  Although  it  does  not 
re(  den  blue  litmus,  it  readily  reacts  with  the  metallic  hydrates, 
for  ning  crystallizable  compounds  which  in  some  respects  resemble 
the  salts.  It  acquires  a  more  or  less  intense  red  color  on  exposure 
to  dr  and  light.  Phenol  is  an  exceedingly  valuable  agent  for  the 
detraction  of  low  forms  of  life.  It  prevents  putrefaction  and 
dei  ay  of  animal  and  vegetable  matters,  because  it  prevents  the 
development  of  the  minute  germs  of  life  which  are  the  cause  of 
such  decompositions.  Phenol  is  poisonous,  and  in  a  concentrated 
for  n  is  quite  corrosive  to  living  animal  tissues. 

When  bromine-water  is  added  to  even  a  very  dilute  solution 
of  phenol,  a  yellow  precipitate  of  tribromophenol,  C6H2Br3(OH), 
is  formed.  A  pine  shaving  dipped  in  phenol  and  then  exposed  to 
the  air  acquires  a  blue  color.  These  properties  aid  us  in  identi- 
fying phenol. 

^Vhen  two  hydrogen  atoms  of  benzol  are  replaced  by  hydroxyl  groups,  di- 
atomic phenols,  usually  called  oxyphenols,  result.  They  naturally  have  the 
composition  C6I14(OH)2.  Three  oxyphenols  are  known,  and  we  have  already 
seen  that  we  can  understand  these  cases  of  isomerism  by  attributing  to  the 
hydroxyl  groups  different  positions  in  the  system  of  carbon  atoms  which  are 
so  intimately  related  together. 

o71.  Trinitrophenol,  C6H2(N02)3.OH,  commonly  called  picric 
acid,  is  obtained  by  boiling  phenol  with  concentrated  nitric  acid. 
C6H5.0H     +     3HN03     =     C6H2(N02)3.OH     +     3H20 


228  LESSONS    IN   CHEMISTRY. 

It  crystallizes  from  its  solution  in  boiling  water  in  small,  lemon- 
yellow  scales,  which  are  not  very  soluble  in  cold  water.  It  has 
an  exceedingly  bitter  taste.  It  has  acid  properties,  for  the  three 
nitryl  groups,  NO2,  seem  to  make  the  hydrogen  of  the  hydroxyl 
more  readily  replaceable  by  metal. 

372.  POTASSIUM  PICRATE,  C6H2(N02)3.OK,  may  be  made  by  adding  potassium 
carbonate  to  a  boiling  solution  of  picric  acid  as  long  as  carbon  dioxide  is  dis- 
engaged.    It  forms  long  yellow  needles,  only  slightly  soluble  in  cold  water. 

373.  AMMONIUM  PICRATE,  C6H2(N02)3.ONH4,  is  obtained  in  a  similar  manner 
by  neutralizing  picric  acid  with  ammonia-water.     It  burns  with  a  flash,  with- 
out leaving  a  residue,  and  has  been  used  in  the  manufacture  of  certain  kinds 
of  gunpowder  and  colored  fires  (§452). 

374.  Nitrobenzol,  C6H5.N02.— When  benzol  is  added  in  small 
portions  to  a  cold  mixture  of  strong  nitric  and  sulphuric  acids, 
and  the  liquid  is  constantly  stirred,  the  benzol  dissolves  ;  when 
the  solution  is  poured  into  cold  water,  a  heavy,  colorless  oil  sepa- 
rates.    This  is  nitrobenzol :  a  hydrogen  atom  of  benzol  has  been 
replaced  by  a  nitryl  group,  NO2. 

C6H6     +     HNO3    =     C6R5.N02     +     H20 

Nitrobenzol  freezes  at  3°,  and  boils  at  205°.  It  has  an  odor 
resembling  that  of  bitter  almonds,  and  is  used  in  perfumery,  es- 
pecially for  imparting  an  odor  to  soap.  It  is  manufactured  in 
large  quantities  for  the  production  of  aniline. 

375.  Aniline,  C6H5.NH2.— If  nitrobenzol  be  treated  with  a 
mixture  capable  of  generating  hydrogen,  the  nitryl  group  is  re- 
duced, and  converted  into  a  group  NH2.     Almost  all  reducing 
agents  produce  this  change,  but  in  the  arts  a  mixture  of  iron 
filings  and  acetic  acid  is  used.     The  hydrogen  eliminated  from 
the  acetic  acid  by  the  iron,  with  formation  of  iron  acetate,  then 
reduces  the  nitrobenzol  to  aniline. 

C«II&.N02     +     3H2     =     C6H5.NH2     +     2H20 
Nitrobenzol.  Aniline. 

The  operation  is  conducted  in  large  cylinders  in  which  the 
nitrobenzol  is  continually  stirred  with  the  acetic  acid  and  iron 
filings.  The  aniline  formed  is  then  distilled. 

Aniline  is  a  colorless  liquid,  but  becomes  brown  on  long  ex- 


ROSANILINE.  229 

posare  to  the  air.  It  has  an  unpleasant  odor,  and  an  acrid,  burn- 
ing taste.  It  is  heavier  than  water,  in  which  it  is  insoluble.  It 
boils  at  184°.  It  is  soluble  in  all  proportions  of  alcohol  and 
eth  ;r.  It  is  not  alkaline  to  litmus,  but  combines  directly  with 
aci<  s,  forming  crystallizable  salts. 

Aniline  represents  ammonia  in  which  one  atom  of  hydrogen  is  replaced  by 
the  tnonatomic  group  C6H5.  All  of  the  hydrocarbon  radicals  are  capable  of 
repl  icing  the  hydrogen  of  ammonia,  and  the  compounds  so  formed  are  called 
con  tound  ammonias,  or  amines.  Thus,  methylamine,  dimethylamine,  and 
trin  ethylamine  are  formed  respectively  by' the  replacement  of  one,  two,  and 
thr<  3  atoms  of  hydrogen  in  a  molecule  of  ammonia. 

NH3  NH^.CH3  NH(CH3)2  N(CH3)3 

Ammonia.          Methylamine.  Dimethylamine.        Trimethylamine. 

T  10  group  C6H5,  which  is  benzol  less  one  atom  of  hydrogen,  is  called^/fe»y, 
and  phenol  is  then  phenyl  hydrate,  while  aniline  is  phenylamine. 

.'  76.  To  a  little  aniline  in  a  test-tube,  we  add  a  crystal  of  potas- 
siu  11  nitrate,  and  then  some  strong  sulphuric  acid ;  a  bright  red 
col«  r  is  produced.  In  another  tube  we  mix  some  aniline  with 
abc  at  twice  its  volume  of  strong  sulphuric  acid,  and  then  drop  in 
a  s  nail  fragment  of  potassium  dichromate  ;  a  magnificent  blue 
col<  r  is  developed,  and  becomes  violet  when  the  mixture  is  diluted 
with  water.  A  little  bleaching-powder,  that  is.  chlorinated  lime, 
add  id  to  aniline  produces  also  a  violet  color.  These  reactions  are 
app  ied  on  a  large  scale  in  the  manufacture  of  numerous  coloring 
matters  derived  from  aniline. 

377.  Rosaniline. — The  benzol  of  commerce  is  not  pure,  it  con- 
tains much  methylbenzol  or  toluol :  when  it  is  converted  succes- 
sively into  nitrobenzol  and  aniline,  a  nitro-derivative  of  toluol  is 
also  formed,  and  this  is  reduced  to  methylaniline,  just  as  the  nitro- 
benzol is  reduced  to  aniline.  When  such  aniline  is  heated  with 
oxidizing  agents,  both  the  aniline  and  the  methylaniline  lose  hydro- 
gen atoms,  and  the  residues  of  the  molecules  combine,  forming  a 
complex  body  called  rosaniline. 

C«IPN     +     2C?H9N     +     O3     =  •     C2°Hi9N3     +     3H20 
Aniline.        Methylaniline.  Rosaniline. 

Large  quantities  of  rosaniline  are  manufactured  by  heating 
commercial  aniline  either  with  arsenic  acid  or  under  pressure  with 

20 


230  LESSONS   IN   CHEMISTRY. 

nitrobenzol ;  the  oxygen  of  the  arsenic  acid  or  of  the  nitrobenzol, 
removes  hydrogen  from  the  aniline. 

Rosaniline  is  a  colorless  substance,  but  its  salts  have  magnificent 
colors  and  are  used  as  dye-stuffs.  The  rich  red  coloring  matter 
called  fuchsine  is  a  compound  of  one  molecule  of  rosaniline  with 
one  of  hydrochloric  acid.  If  a  hot  saturated  solution  of  this  body 
be  treated  with  sodium  hydrate,  the  color  disappears  ;  sodium 
chloride  is  formed,  and  rosaniline  separates  as  an  almost  colorless, 
crystalline  precipitate. 

The  hydrogen  atoms  of  rosaniline  may  be  replaced  by  various 
monatomic  radicals,  such  as  methyl,  ethyl,  phenyl.  The  com- 
pounds formed  by  three  such  replacements  are  more  easily  obtained 
than  the  others,  and  the  salts  of  the  resulting  tri-substituted 
rosaniiines  constitute  a  numerous,  varied,  and  valuable  class  of 
coloring  agents,  known  as  the  aniline  dyes. 


LESSON    XLV. 

BENZOL  DERIVATIVES   (2). 

378.  The  hydrocarbons  derived  from   benzol   by  the   replace- 
ment of  its  hydrogen  atoms  by  groups  such  as  methyl  or  ethyl, 
are  capable  of  forming  both  phenols  and  alcohols ;  for  if  the  re- 
placement of  a  hydrogen   atom   by  hydroxyl   be  in   the  benzol 
radical,  a  phenol  would  result,  while  an  alcohol  would  be  formed 
by  such  a  replacement  in  the  methyl  or  ethyl  group.     Methyl- 
benzol  or  toluol  can  thus  form  an  alcohol,  called  benzyl  alcohol, 
and  three  isomeric  phenols,  which  are  called  cresols. 

C6H5-CH3  HO.C6H*.(CH3)  C6H5.CH2.0H 

Methyl  benzol.  Cresols.  Benzyl  alcohol. 

Our  time  will  permit  the  study  of  only  a  few  of  these  com- 
pounds. 

379.  Benzyl  Aldehyde,  C6H5.CHO.— When  chlorine  gas  is 


SALICYLIC   ALDEHYDE. 


231 


passed  through  boiling  toluol,  benzyl  chloride,  C6H5-CH2C1,  is 
formed,  and  by  alkaline  hydrates  this  may  be  converted  into  benzyl 
alcohol,  C6H5-CH2.OH.  Just  as  ordinary  alcohol  may  by  slow 
oxidation  be  converted  into  aldehyde,  benzyl  alcohol  is  by  the 
action  of  nitric  acid  converted  into  benzyl  aldehyde.  The  latter 
body  is  interesting,  because  it  is  the  essential  part  of  oil  of  bitter 
ah  '.onds,  so  much  used  for  flavoring.  The  oil  of  bitter  almonds 
is,  however,  poisonous,  for  it  contains  hydrocyanic  acid,  which,  to- 
ge~  her  with  benzyl  aldehyde,  results  .from  the  action  of  water  on 
a  substance  called  amygdalin,  existing  in  the  almonds. 

$80.  Benzole  Acid,  C6H5.CO.OH,  exists  naturally  in  gum  ben- 
zoi  i,  and  is  the  product  of  the  oxidation  of  benzyl  aldehyde  and 
be  zyl  alcohol.  It  may  be  easily  prepared  from  gum  benzoin,  by 
ge  tly  heating  some  of  that  resin  in  a  shallow  dish,  over  which  is 
pa  ted  a  piece  of  filter-paper. 
W ;  cover  the  dish  with  a 
be:  ker,  and  the  vapor  of  ben- 
zoi3  acid  passes  through  the 
pa  >er,  on  which  and  in  the 
be;  ker  it  condenses  in  beauti- 
ful feathery  tufts  (Fig.  99). 

Benzoic  acid  crystallizes  in 
col  )rless  needles  or  thin  plates. 
It  melts  at  121°,  and  boils  at 
25  )°.  It  is  not  very  soluble 
in  .'old  water,  but  dissolves  in 
about  twelve  times  its  weight 
of  boiling  water,  and  is  also 
soluble  in  alcohol.  It  is  an 
excellent  antiseptic  or  pre- 
servative. 

381.  Salicyl  Aldehyde,  C6H*(OH).CHO.—  The  pleasant 
odor  of  essential  oil  of  meadow-sweet  is  due  to  a  compound  repre- 
senting benzyl  aldehyde  in  which  an  atom  of  hydrogen  in  the 
benzol  group  is  replaced  by  the  radical  hydroxyl.  It  is  at  the 
same  time  an  aldehyde  and  a  phenol.  It  is  a  colorless  liquid, 


FIG.  99. 


232  LESSONS   IN    CHEMISTRY. 

boiling  at  196°.     It  is  heavier  than  water.     Oxidizing   agents 
convert  it  into 

Salicylic  Acid,  C6H4(OH)CO.OH,  in  which  the  group  CHO 
of  the  aldehyde  has  been  changed  to  carboxyl,  CO. OH.  Salicylic 
acid  is  now  manufactured  by  the  action  of  carbon  dioxide  on 
phenol,  or,  more  correctly,  sodium  phenate.  We  may  represent 
the  reaction 

C6H5.0H         +        CO2        -        C6H4(OH)CO.OH 
Phenol.  Salicylic  acid. 

Salicylic  acid  occurs  as  methyl  salicylate  in  oil  of  wintergreen : 
the  basic  hydrogen,  that  of  the  hydroxyl  group,  is  here  replaced 
by  a  methyl  group,  CH3. 

C6H4(OH).CO.OH  C«H*(OH).CO.OCH3 

Salicylic  acid.  Methyl  salicylate. 

When  oil  of  wintergreen  is  boiled  with  potassium  hydrate, 
potassium  salicylate  and  methyl  alcohol  are  formed. 

C6H*(OH)CO.OCH3     +     KOH    =     C6H4(OH)CO.OK     +     CH3.OH 

Salicylic  acid  crystallizes  in  needles  or  prisms  which  are 
scarcely  soluble  in  cold  water,  but  very  soluble  in  boiling  water, 
alcohol,  and  ether.  It  is  largely  used  as  a  preservative,  and  to 
some  extent  in  medicine. 

382  Gallic  Acid,  C6H2(OH)3.CO.OH.— Salicylic  acid  repre- 
sents benzoic  acid  in  which  one  atom  of  hydrogen  is  replaced  by 
a  hydroxyl  group.  It  is  a  phenol  and  an  acid.  Gall-nuts,  which 
are  little  excrescences  produced  by  the  sting  of  an  insect  on  the 
leaves  and  twigs  of  certain  species  of  oak,  contain  a  substance 
which,  by  continued  exposure  to  air  and  moisture,  undergoes  a 
sort  of  fermentation.  When  the  liquid  is  pressed  from  the  dark- 
colored  mass,  there  remains  a  compound  which  may  be  crystallized 
from  boiling  water  in  long,  colorless,  silky  needles.  It  is  gallic 
acid,  a  compound  which  we  may  consider  as  benzoic  acid  in  which 
three  hydrogen  atoms  are  replaced  by  three  hydroxyl  groups.  It 
is  colorless  and  odorless.  When  carefully  heated  to  100°,  it  is 
converted  into  a  white  volatile  substance  known  as  pyrogallol,  or 
pyrogallic  acid,  while  at  the  same  time  carbon  dioxide  is  disengaged. 

C«H2(OH)3.CO.OH         =         C6H3(OH)3         +         CO2 
Gallic  acid.  Pyrogallol. 


TANNIN.  233 

Grallic  acid  is  very  soluble  in  boiling  water  ;  not  very  soluble  in 
cold  water.  Its  solutions,  especially  if  an  alkaline  hydrate  be 
pr<  sent,  absorb  oxygen  from  the  air,  and  become  dark  in  color. 
Tl  is  last  property  is  also  common  to  pyrogallol,  a  solution  of 
wl  ich  is  used  as  a  reducing  agent  in  photography. 

383.  Tannin.  —  The  well-known  astringent  properties  of  certain 
pi;  nts  are  due  to  the  presence  of  compounds  known  as  tannins  or 
tannic  acids,  of  which  there  appear  to  be  a  number  of  varieties. 
Tl  ey  possess  the  property  of  coagulating  albumen  and  gelatin,  and 
of  forming  black  or  nearly  black  precipitates  with  salts  of  iron. 
T;  nnin  may  be  extracted  from  gall-nuts  by  placing  the  coarsely- 
pt  vvdered  nuts  in  a  funnel  and  pouring  through  them  ether  which 
is  not  free  from  water.  As  the  ether  runs  through,  it  retains  the 
co  oring  matters,  while  the  water  in  the  ether  dissolves  the  tan- 
ni  i,  and  the  aqueous  solution  separates  from  the  layer  of  ether 
01  standing.  When  this  solution  is  evaporated  at  a  gentle  heat, 
th  3  tannin  remains  as  a  light,  very  porous  mass.  It  has  an 
as  ringent  taste,  and  is  very  soluble  in  water.  When  exposed  to 
in  »ist  air,  it  is  converted  into  gallic  acid  ;  a  temperature  of  about 
210°  decomposes  it,  with  formation  of  pyrogallol  and  carbon 
di  »xide.  These  reactions  indicate  that  tannin  is  related  to  gallic 
ac  d,  and  at  least  one  of  its  varieties  appears  to  be  formed  by  the 
union  of  two  molecules  of  gallic  acid  with  the  loss  of  one  molecule 
of  water.  It  is  then  digallic  acid. 


Gallic  acid.  Digallic  acid. 

The  black  mixture  obtained  by  mixing  solutions  of  tannin  with 
feiric  salts  constitutes  ink.  A  good  black  ink  may  be  made  by 
exhausting  100  grammes  of  powdered  gall-nuts  with  1.4  litres  of 
water,  and  adding  to  the  filtered  liquid  a  solution  of  50  grammes 
of  gum  arabic  and  50  grammes  of  ferrous  sulphate,  each  in  the 
least  quantity  of  water  which  will  dissolve  it.  After  stirring  the 
mixture,  it  is  allowed  to  stand  exposed  to  the  air  until  it  becomes 
quite  black. 

The  operation  of  tanning,  or  the  conversion  of  animal  skins  into 
leather,  depends  on  the  formation  in  the  skin  of  an  insoluble  com- 

20* 


234  LESSONS   IN   CHEMISTRY. 

pound  of  tannin  and  the  albuminoid  matter  of  the  skin.  The 
tannin  is  derived  from  oak  bark,  which  is  ground  to  a  coarse  pow- 
der and  piled  in  alternate  layers  with  the  skins  in  deep  vats. 
The  vats  are  then  filled  with  water,  and  the  skins  are  allowed  to 
soak  for  a  few  weeks  or  months,  until  they  have  become  thoroughly 
penetrated  by  the  tannin. 

384.  Camphors. — The  highly  aromatic  solids  that  constitute 
the  class  of  bodies  called  camphors  are  derived  from  a  methyl-pro- 
pyl-benzol  called  cymene  ;  it  is  benzol  in  which  two  atoms  of  hy- 
drogen have  been  replaced,  one  by  a  methyl  group,  CH3,  the  other 
by  a  propyl  group,  C3H7.     Its  composition  is  therefore  C10HU. 

C6H6  C6H*(CH3)(C3H7) 

Benzol.  Cymene. 

Cymene  exists  naturally  in  the  essential  oils  of  chamomile  and 
thyme.  It  is  a  liquid  having  a  pleasant  odor.  Its  relations  to 
the  series  of  camphors  are  indicated  in  the  following  formulae : 

C10IP*,  Cymene. 

C10HU0,  Thymol,  or  thyme  camphor. 

C10H160,  Camphol,  or  ordinary  camphor. 

C10I1180,  Borneol,  or  Borneo  camphor. 

C10H200,  Menthol,  or  mint  camphor. 

385.  THYMOL,  C10HU0,  is  a  phenol,  one  of  the  hydrogen  atoms 
of  the  benzol  group  in  cymene  being  replaced  by  the  group  OH. 
It  exists  in  the  essential  oil  of  thyme,  from  which  it  may  be  ex- 
tracted in  the  form  of  large,  colorless,  crystalline  plates,  fusible  at 
44°.     It  has  a  pleasant  but  penetrating  odor,  and  is  an  excellent 
preservative,  for  it  has  antiseptic  properties,  destroying  low  forms 
of  life. 

386.  CAMPHOL,  C10H160,  is  ordinary  camphor,  sometimes  called 
laurel  camphor,  because  it  is  obtained  from  the  camphor  laurel,  a 
tree  of  China,  Japan,  and  the  Sunda  Isles.     It  exists  in  all  parts 
of  the  tree,  but  is  extracted  from  the  wood,  which  is  chopped  in 
small  pieces  and  distilled  with  water.     The  camphor  vapor  con- 
denses on  rice-straw,  with  which  the  head  of  the  still  is  filled :  it 
is  removed,  and  purified  by  a  new  sublimation.     It  forms  semi- 
transparent,  crystalline  masses  having  a  strong,  aromatic  odor  and 
a  sharp,  burning  taste.     Its  density  at  0°  is  1.     It  melts  at  175°, 


INDIGO.  235 

and  boils  at  204°  ;  it  is  exceedingly  volatile,  and  even  at  ordinary 
temperatures  it  sublimes  in  the  vessels  in  which  it  is  kept,  con- 
dei  sing  in  the  upper  part  in  brilliant,  colorless  crystals.  It  is 
aln  ost  insoluble  in  water,  but  dissolves  readily  in  alcohol  and  in 
eth.jr.  When  small  fragments  of  camphor  are  thrown  on  the  sur- 
f'ac  ;  of  clean  water,  they  move  around  with  curious  gyratory  move- 
mi  its,  which  are  caused  by  the  pressure  of  the  camphor  vapor 
gh  en  off  in  unequal  quantities  from  different  parts  of  the  surface 
of  the  fragments.  The  currents  of -vapor  may  be  made  evident 
by  dusting  a  small  quantity  of  the  fine  powder  called  lycopodium 
on  the  surface  of  the  water. 

:  187.  BORNEOL,  C10H180,  is  obtained  from  an  aromatic  tree  of 
th(  Sunda  Isles.  It  forms  small  colorless  crystals,  having  an  odor 
lik  that  of  camphor,  but  at  the  same  time  resembling  that  of 
pe)  per.  It  is  insoluble  in  water,  but  dissolves  in  both  alcohol  and 
etI'Br.  Strong  nitric  acid  converts  it  into  ordinary  camphor. 

:;88.  MENTHOL,  C10H200,  is  the  solid  part  of  the  essential  oil 
of  nint,  in  which  it  is  mixed  with  a  hydrocarbon  having  the  same 
COL  (position  as  oil  of  turpentine.  It  forms  colorless  crystals, 
fus"  bleat  36°. 

:  89.  Indigo,  C16H10N202,  is  prepared  from  several  indigo 
plants,  which  are  cultivated  principally  in  India.  The  leaves  and 
stens  of  these  plants  are  soaked  in  water  for  a  day  or  two ;  a  sort 
of  ^ermentiition  takes  place,  after  which  the  liquid  is  expressed 
and  agitated  in  contact  with  the  air.  A  blue  deposit  forms ;  it  is 
collected  and  boiled  with  water  in  large  copper  vessels,  and  then 
drained,  pressed,  and  broken  up  into  the  fragments  in  which  in- 
digo occurs  in  commerce.  Indigo  results  from  the  decomposition 
of  cue  of  its  compounds  which  exists  in  the  plant. 

The  best  indigo  has  a  coppery  appearance.  It  is  not  perfectly 
pure,  but  a  small  quantity  may  be  purified  by  gently  heating  it  in 
a  small  flask  through  which  hydrogen  is  passed  :  the  pure  indigo, 
which  is  called  indigotm,  then  sublimes  and  condenses  in  small 
crystals  around  the  cooler  portions  of  the  flask.  It  is  insoluble  in 
water,  alcohol,  and  ether,  but  dissolves  in  strong  sulphuric  acid, 
especially  in  fuming  sulphuric  acid.  The  dark-blue,  solution  so 


236  LESSONS    IN    CHEMISTRY. 

obtained  is  commonly  called  sulphate  of  indigo,  and  is  used  in 
dyeing. 

390.  WHITE  INDIGO,  C16H12N202.— When  indigo  is  subjected 
to  the  action  of  reducing  agents,  such  as  sulphurous  acid  and  hy- 
drogen sulphide,  it  is  converted  into  a  dirty-white  substance  called 
white  indigo.  If  a  mixture  of  indigo,  ferrous  sulphate,  and  milk 
of  lime  be  shaken  in  a  corked  bottle,  and  allowed  to  stand  for  a 
day  or  two,  an  alkaline  solution  of  white  indigo  is  obtained,  from 
which  the  latter  may  be  precipitated  by  a  current  of  hydrochloric 
acid  gas.  The  white  indigo  is  insoluble  in  water,  but  dissolves  in 
alcohol  and  in  solutions  of  the  alkaline  hydrates.  If  a  white 
cloth  be  dipped  in  the  yellowish  solution  in  the  bottle,  and  then 
exposed  to  the  air,  it  rapidly  becomes  blue.  White  indigo,  which 
is  a  compound  of  hydrogen  with  indigo,  is  again  converted  into 
indigo  on  contact  with  the  air,  and  the  experiment  with  the  cloth 
is  an  illustration  of  the  manner  in  which  in  dyeing  the  insoluble 
blue  indigo  is  deposited  in  the  tissues  of  fabrics. 

Indigo  has  been  obtained  artificially  by  a  number  of  interesting 
reactions,  which  will  ere  long  permit  the  manufacture  of  this 
important  dye-stuff  from  the  hydrocarbons  of  coal-tar. 


LESSON    XLVL 

NATURAL   ALKALOIDS. 

391.  The  compound  ammonias,  derived  from  ammonia  by  re- 
placement of  one  or  more  of  its  hydrogen  atoms  by  various  groups 
or  radicals,  are  powerful  bases.  They  combine  directly  with  acids, 
forming  definite  crystallizable  salts.  Thus,  methyl  ammonium 
chloride  is  as  definite  a  body  as  ammonium  chloride  or  potassium 
chloride. 

KCl  NH4.C1  NH»(CH»).CI 

Potassium  chloride.  Ammonium  chloride.  Methylammonium  chloride. 

An  immense  number  of  compound  ammonias  have  been  formed, 


CONINE.  237 

and  well  studied,  so  that  their  molecular  constitutions  are  perfectly 
kn<  wn.  Many  plants  contain  principles  which  we  have  not  been 
abb'  to  obtain  artificially,  but  which  so  much  resemble  the  com- 
poi  nd  ammonias  in  their  chemical  relations  that  we  believe  them 
to  belong  to  the  same  class.  They  all  contain  nitrogen,  and  it  is 
to  ihe  nitrogen  atom  or  atoms  that  are  due  the  basic  properties  of 
thi  compounds  which  are  called  natural  alkaloids;  that  is,  alkaline- 
lik<  bodies.  Most  of  these  substances  are  poisonous  ;  they  all  exert 
PCM  uliar  and  active  effects  on  the  animal  economy. 

192.  The  processes  adopted  for  the  separation  of  the  alkaloids 
fro  n  the  plants  or  vegetable  products  in  which  they  occur,  vary 
ace  :»rding  to  the  solubility  of  the  particular  alkaloid  and  its  salts 
in  various  solvent  agents.  The  alkaloids  do  not  occur  in  an  un- 
coi  ibined  state  in  the  plants,  but  united  with  some  natural  acid 
wii  h  which  they  form  salts.  If  the  natural  salt  be  soluble  in  water, 
an  aqueous  extract  of  the  compound  may  be  used  for  the  prepara- 
tio  i  of  the  alkaloid,  but  usually  very  dilute  sulphuric  acid  is  em- 
pl<  yed  ;  sometimes  the  plant  or  product  must  be  extracted  with 
ale  >hol.  The  alkaloid  is  then  set  free  by  the  addition  of  milk 
of  lime  or  other  alkaline  hydrate,  which  will  form  a  salt  with  the 
natural  acid:  sometimes  the  salt -formed  is  insoluble  in  the  liquid 
em  aloyed,  while  the  alkaloid  dissolves;  sometimes  it  is  the  alka- 
loid which  is  insoluble  and  the  salt  which  remains  in  solution. 
Th  .se  circumstances  must  be  investigated,  and  such  a  process 
adopted  as  will  allow  the  alkaloid  to  be  entirely  separated,  and  it 
can  then  be  easily  purified  by  crystallization. 

Two  important  natural  alkaloids  are  liquid ;  they  are  conine 
and  nicotine. 

o93.  Conine,  C8H15N,  is  the  active  principle  of  poisonous 
hemlock.  It  is  extracted  from  the  seeds,  which  are  crushed  and 
distilled  with  an  alkaline  hydrate.  The  conine  distils,  and  is 
neutralized  with  sulphuric  acid,  which  converts  it  into  a  sulphate, 
of  which  the  solution  is  evaporated  to  a  syrupy  consistence,  and 
then  exhausted  with  a  mixture  of  alcohol  and  ether.  When  the 
alcohol  and  ether  have  been  evaporated,  the  conine  sulphate  is 
distilled  with  a  strong  solution  of  sodium  hydrate,  and  sodium 


238  LESSONS   IN   CHEMISTRY. 

sulphate  is  formed,  while  the  conine  set  free  condenses,  together 
with  a  little  water.  The  conine  may  be  dried  by  calcium  chloride. 
It  is  a  colorless,  oily  liquid,  having  a  disgusting  odor.  It  is  only 
slightly  soluble  in  cold  water,  and  still  less  soluble  in  hot  water, 
but  dissolves  freely  in  alcohol  and  ether.  It  is  very  poisonous,  as 
are  also  its  salts. 

394.  Nicotine,  C10HUN2,  exists  in  tobacco,  probably  in  combi- 
nation with  malic  acid.     It  may  be  obtained  by  extracting  tobacco 
with  boiling  water,  evaporating  the  filtered  solution  until  it  becomes 
a  pasty  mass,  and  mixing  this  residue  with  about  twice  its  volume 
of  alcohol.     The  alcoholic  liquid  separates  in  two  layers,  of  which 
the  upper  contains  the  nicotine :  it  is  decanted,  and  the  alcohol 
distilled  off.     From  the  residue  the  nicotine  is  set  free  by  potas- 
sium hydrate,  and  dissolved  out  by  ether.     The  impure  nicotine 
may  then  be  converted  into  an  oxalate  by  the  addition  of  oxalic 
acid,  and  when  this  is  decomposed  by  potassium  hydrate,  tolerably 
pure  nicotine  is  obtained. 

Nicotine  is  a  colorless  liquid,  having  an  irritating  and  most 
penetrating  odor.  It  is  very  soluble  in  water,  alcohol,  and  ether. 
It  boils  between  240°  and  250°.  It  is  an  energetic  base,  and  is 
one  of  the  most  active  poisons  known.  Tobacco  contains  from 
two  to  about  seven  per  cent,  of  nicotine,  the  most  esteemed  varieties 
being  those  which  contain  the  least. 

395.  Theobromine,  C7H8N402,  is  the  alkaloid  of  cacao,  and 
may  be  extracted  from  cacao  beans.     It  is  a  white,  crystalline 
powder,  having  a  bitter  taste,  and  is  not  very  poisonous. 

396.  Caffeine,  C8HION402,  sometimes  called  theine,  exists  in 
coffee,  tea,  and  several  other  plant  products.     It  may  be  prepared 
by  making  a  strong  tincture  of  tea  with  cold  alcohol,  and  precipi- 
tating the  filtered  liquid  with  basic  lead  acetate.     The  mixture  is 
filtered,  and  freed  from  lead  by  a  stream  of  hydrogen  sulphide, 
after  which  it  is  again  filtered,  evaporated  to  a  small  volume,  and 
while  still  hot  is  treated  with  potassium  hydrate.     Caffeine  then 
crystallizes  out  as  the  liquid  cools.     It  forms  long,  brilliant,  white 
needles,  containing  one  molecule  of  water  of  crystallization,  which 
is  driven  out  by  a  temperature  of  100°.     It  has  a  bitter  taste; 


MORPHINE. — QUININE.  239 

it  is  not  very  soluble  in  cold  water,  but  dissolves  readily  in  hot 
water  and  in  alcohol. 

397.  Morphine,  C17H19N03.— Opium,  which  is  the  thickened 
jui  ;e  of  the  unripe  capsules  of  the  opium  poppy,  contains  several 
alk;  loids,  of  which  the  most  important  is  morphine.     The  natu- 
ral salts  in  which  these  alkaloids  exist  in  opium  are  soluble  in 
alc<  hoi  ;  laudanum  and  paregoric  are  tinctures  of  opium.     Mor- 
phi  le  may  be  most  easily  extracted  by  making  a  cold  watery  ex- 
tra* t  of  finely-cut    opium,  evaporating  the    filtered    liquid,  and 
adt;  ing  sodium  carbonate  to  the  still  hot  syrup.     In  the  course  of 
a  d  iy  morphine  deposits,  and  may  be  collected  on  a  filter  and  dis- 
sob  ed  in  a  little  dilute  acetic  acid.     The  filtered  solution  is  then 
dec  )lorized  by  animal  charcoal,  and  the  morphine  again  precipi- 
tatt  d  by  ammonia.     Morphine  is  almost  insoluble  in  water,  and 
ins*  luble  in  ether.     It  is  dissolved  by  hot  alcohol,  from  which  it 
sep  irates  in  crystals  containing  one  molecule  of  water.     It  has  a 
ver  *  bitter  taste. 

"  Vhen  nitric  acid  is  added  to  a  little  morphine,  an  orange-red 
col<  r  is  produced.  Ferric  chloride  solution  produces  a  blue  color 
wit  i  morphine.  Morphine  forms  easily-crystallizable  salts ;  the 
sul]  hate,,  chloride,  and  acetate  are  used  in  medicine ;  these  salts 
are  soluble  in  water. 

The  principal  alkaloids  of  opium,  besides  morphine,  are  codeine, 
C18H21N03,  and  narcotine,  C22H23N07 ;  both  are  crystallizable 
solitls.  Codeine  is  morphine  in  which  one  hydrogen  atom  is 
replaced  by  methyl. 

398.  Cocaine,  017H21N04,  exists  in  coca  leaves,  which  are  much 
used  as  a  tonic  and  stimulant  in  South  America. 

399.  Atropine,  C17H23N03,  is  the   alkaloid  of  belladonna  or 
deadly  nightshade,  and  is  identical  with  daturine,  the  poisonous 
principle    of    stramonium,    commonly    called    Jamestown    weed. 
When  it  is  administered  internally,  or  applied  to  the  eye,  it  pro- 
duces dilatation  of  the  pupil,  which  continues  until  all  of  the  alka- 
loid has  passed  from  the  system.     It  is  exceedingly  poisonous. 

400.  Quinine,  C20H24N202.— Cinchona  bark,  universally  known 
and  used   as  a  remedy,  contains  several   alkaloids,  the  more  im- 


240  LESSONS    IN   CHEMISTRY. 

portant  being  quinine  and  cinchonine.  These  alkaloids  are  almost 
insoluble  in  water,  and  their  sulphates  are  the  forms  in  which  they 
are  principally  employed  in  medicine.  For  the  manufacture  of 
these  salts,  the  bark  is  extracted  with  water  acidulated  with  sul- 
phuric acid,  and  the  addition  of  milk  of  lime  to  the  clear  solution 
causes  the  precipitation  of  the  insoluble  alkaloids,  mixed  with 
calcium  sulphate  and  the  excess  of  lime.  The  deposit  is  collected, 
dried,  and  exhausted  with  boiling  alcohol,  which  dissolves  the  al- 
kaloids. When  the  filtered  alcoholic  solution  is  evaporated,  the 
cinchonine  crystallizes  first,  being  least  soluble,  and  the  quinine  is 
then  neutralized  with  sulphuric  acid,  and  the  solution  concentrated 
until  the  sulphate  crystallizes. 

Quinine  sulphate  crystallizes  in  very  bitter,  delicate  white 
needles,  only  slightly  soluble  in  cold  water,  but  dissolving  in  about 
thirty  times  their  weight  of  boiling  water.  It  dissolves  readily  in 
water  containing  a  little  free  acid.  When  ammonia  is  added  to 
its  solution,  the  free  alkaloid  quinine  is  precipitated  as  a  white 
powder,  while  ammonium  sulphate  is  formed.  Quinine  is  soluble 
in  about  its  own  weight  of  alcohol,  and  in  twenty-two  times  its 
weight  of  ether.  It  is  almost  insoluble  in  water. 

401.  Cinchonine,  C20H24N20,  is  deposited  from  the  alcoholic 
solution  in  which  quinine  still  remains  in  solution  during  its  ex- 
traction from  cinchona  bark.     Its  properties  much  resemble  those 
of  quinine,  from  which,  however,  it  may  be  distinguished  by  its 
insolubility  in  ether.     Quinine  sulphate  supposed  to  contain  cin- 
chonine sulphate  is  treated  with  a  little  ammonia-water,  and  then 
agitated  with  ether;  any  cinchonine   present  will  remain  undis- 
solved. 

402.  Strychnine,  C21H22N202.— The  poisonous  and  medicinal 
properties  of  nux  vomica  are   due   principally  to  two  alkaloids, 
strychnine  and  brucine.     They  are  almost  insoluble  in  water,  and 
may  be  extracted  from  nux  vomica  by  a  process  like  that  which 
serves  for  the  separation  of  quinine.     They  are  both  exceedingly 
bitter,  crystallizable  solids,  nearly  insoluble  in  water.     Strychnine 
is  almost  insoluble  in  alcohol  and  ether,  but  dissolves  in  chloro- 
form.    Brucine  is  soluble  in  alcohol,  and  somewhat  soluble  in  ether. 


METALS.  241 

If  a  small  fragment  of  potassium  dichromate  is  placed  beside 
a  crystal  of  strychnine,  and  both  are  touched  with  a  drop  of  sul- 
phuric acid,  a  rich  blue  color  is  produced,  which  quickly  changes 
to  violet,  purple,  and  red,  and  finally  fades. 

Strychnine  is  a  violent  poison  ;  when  taken  even  in  compara- 
th  ely  trifling  quantities,  it  produces  terrible  convulsions,  resem- 
bl  ng  those  of  tetanus. 


LESSON    XLVII. 
METALS.— SPECTRUM  ANALYSIS. 

403.  The  classi6cation  of  the  elements  as  metals  and  non- 
iii  .tals  is  more  for  the  sake  of  convenience  than  for  the  indication 
of  absolute  properties  of  either  class.  We  may,  however,  consider 
th  xt  certain  general  properties  are  peculiarly  manifested  by  the 
m  ;tals :  they  are  good  conductors  of  heat  and  electricity ;  they 
ar ;  capable  of  acquiring  a  brilliant  lustre,  which  is  called  the 
m  Gallic  lustre.  These  properties  are,  however,  more  or  less  de- 
ve  oped  in  some  of  the  elements  which  we  have  already  studied. 
It  is  not  so,  however,  with  a  chemical  property :  the  metals  are 
capable  of  replacing  the  hydrogen  of  the  oxygen  acids,  forming 
salts.  Some  of  these  salts  we  have  already  studied,  and  we  have 
seen  how  the  combining  power  or  worth  of  a  metallic  atom  is 
indicated  by  the  number  of  hydrogen  atoms  which  it  is  able  to 
replace  in  an  acid.  Yet  even  in  this  respect  the  metals  and  non- 
metals  do  not  seem  to  be  widely  separated,  for  antimony,  which  is 
so  closely  related  to  phosphorus  and  arsenic  by  the  compositions 
and  chemical  natures  of  its  compounds,  is  also  capable  of  forming 
a  i'ew  salts. 

The  physical  properties  of  the  metals  are  most  varied.  They 
are  opaque ;  but  many  of  them  can  be  reduced  to  sheets  so  thin 
that  they  allow  the  passage  of  a  faint  light  whose  color  depends 
on  the  metal  employed.  Their  densities  vary  from  0.59,  that  of 
lithium,  to  22.4,  of  osmium;  their  freezing  points,  from  39°  below 

L  q  21 


242  LESSONS    IN   CHEMISTRY. 

0°,  where  mercury  freezes,  to  about  2500°.  Some,  like  manga- 
nese and  chromium,  are  hard  enough  to  scratch  glass ;  others  are 
soft  enough  to  be  scratched  and  even  cut  by  the  finger-nail,  like 
potassium,  sodium,  and  lead.  Most  of  the  metals  are  malleable  and 
ductile;  they  can  be  beaten  or  rolled  into  sheets  and  drawn  into 
wires.  All  the  metals  are  insoluble  in  water. 

404.  Natural  State  of  the  Metals.— The  condition  in  which 
the  metals  are  encountered  in  nature  depends  upon   the  other 
elements  for  which  they  have  strong  affinities.     Some  of  them 
are  often  found  in  the  metallic  state :  among  these  are  gold,  silver, 
copper,  and  bismuth  ;  they  are  then  called  native  metals, 

In  general,  the  elements  which  are  more,  usually  combined  with 
the  metals  in  their  ores  are  oxygen,  sulphur,  and  chlorine.  Iron, 
zinc,  and  manganese  are  found  as  oxides ;  iron,  copper,  lead,  mer- 
cury, zinc,  and  silver,  as  sulphides;  sodium  and  silver,  as  chlorides; 
calcium  and  magnesium,  as  carbonates ;  aluminium,  as  silicate. 

The  process  adopted  for  the  extraction  of  a  metal  must  of  course 
depend  upon  the  nature  of  its  ores :  oxides  are  heated  with  char- 
coal ;  carbonates  are  first  heated  to  drive  off  carbon  dioxide,  and  the 
resulting  oxide  is  reduced  by  charcoal.  Sulphides  are  roasted, — 
that  is,  heated  in  the  air, — by  which  the  sulphur  is  converted  into 
sulphur  dioxide,  and  passes  off  in  that  gas,  while  an  oxide  of  the 
metal  is  formed.  The  methods  employed  for  the  reduction  of  the 
chlorides  differ  according  to  the  metal. 

405.  Alloys  are  the  compounds  or  mixtures  which  the  metals 
form  with  one  another.     In  the  molten  state,  many  of  the  metals 
are  capable  of  mixing  with  one  another  in  all  proportions ;  but  by 
certain  precautions,  and   the  use  of  the  proper  proportions  of 
metals,  many  alloys  become  crystallizable,  and  assume  the  proper- 
ties of  true  chemical  compounds  :  such  compounds,  of  course,  con- 
tain their  respective  metals  in  the  proportions  required  by  the 
atomic  weights.     The  alloys  of  mercury  are  called  amalgams. 

SPECTRUM   ANALYSIS. 

406.  When  a  ray  of  white  light  is  passed  through  a  prism,  it 
is  dispersed  or  separated  into  a  spectrum   consisting  of  all   the 


SPECTRUM   ANALYSIS.  243 

colors,  from  red  to  violet.  If  the  ray  be  narrow  and  rectangular, 
such  as  is  obtained  by  excluding  all  light  except  that  which 
passes  through  a  rectangular  slit,  and  the  spectrum  be  thrown  on 
a  vvhite  screen,  the  colors  will  not  be  confused,  nor  will  they  be 
distinctly  separate,  but  will  blend  gradually  from  red  to  orange, 
yt  How,  green,  blue,  indigo,  and  violet.  When  any  solid  substance 
is  heated  to  bright  incandescence,  it  emits  a  white  light,  whose 
s]  ectrum  will  contain  all  the  prismatic  colors.  We  have  already 
h  d  occasion  to  observe  the  dazzling  whiteness  of  the  combustion 
OJ  magnesium  and  phosphorus.  We  have  seen,  also,  that  an  alco- 
h"lic  solution  of  boric  acid  burns  with  a  green  flame.  We  may 
prepare  alcoholic  solutions  of  sodium  chloride,  strontium  chloride, 
at  d  barium  chloride,  by  shaking  those  substances  in  separate 
b  ttles  with  alcohol  which  is  not  too  strong.  When  we  burn 
ti  ese  solutions,  we  find  that  the  flame  is  colored  yellow  by  the 
s»  dium  salt,  red  by  that  of  strontium,  and  green  by  that  of 
b  rium,  small  quantities  of  the  salts  being  carried  into  the  vapor 

0  alcohol,  and  volatilized  by  the  high  temperature  of  the  flame. 

1  on  the  end  of  a  small  platinum  wire  we  introduce  separately  a 
li  tie  of  each  of  these  salts  into  the  flame  of  an  alcohol  lamp,  or, 
better,  that  of  a  Bunsen  burner,  we  find  that  the  same  coloration 
is  produced.     If  the  light  from  such  a  flame  be  passed  through  a 
nurrow  slit,  and  then  through  a  prism,  we  find  that  the  color  is 
invariable  for  each  substance.     The  sodium  salt  produces  not  only 
a  yellow  light,  but  a  particular  shade  of  yellow,  which,  because  it 
has  passed  through  the  straight  slit,  forms  a  peculiar  spectrum, 
consisting  of  a  single  line  of  yellow  light.     If  we  keep  the  slit 
and  prism  in  the  same  positions,  it  matters  not  what  compound 
of  sodium  we  introduce  into  the  flame,  the  same  yellow  line  is 
always  produced,  and  on  the  same  part  of  the  screen.     If  we  in- 
troduce a  little  lithium  chloride  into  the  flame,  the  latter  will  be 
colored  red,  and  we  will  find  on  the  screen  a  red  line  of  a  fixed 
and  constant  shade,  and  always  in  the  same  position. 

Analogous  facts  have  been  discovered  for  all  the  elements,  and 
we  may  say,  generally,  that  while  the  light  emitted  by  an  incan- 
descent solid  depends  upon  the  temperature,  being  first  dull  red, 


244 


LESSONS    IN    CHEMISTRY. 


then  orange,  yellow,  and  white,  an  incandescent  gas  or  vapor,  on 
the  contrary,  always  emits  light  of  a  constant  color,  depending 
on  the  nature  of  the  substance.  Usually  the  spectrum  of  an 
element  does  not  consist  of  a  simple  line,  one  color  only,  but  of 
several  and  sometimes  many  lines ;  but  in  each  case  the  spectrum 
is  peculiar  to  the  element. 

407.  These  principles  have  been  applied  in  spectroscopic  anal- 
ysis for  the  detection  of  the  elements,  and  the  instrument  em- 
ployed is  called  a  spectroscope.  It  consists  of  a  narrow  slit  at  the 
end  of  a  metallic  tube  containing  a  lens  (A,  Fig.  100),  by  which 


FIG.  100. 

the  rays  of  light  are  made  to  enter  a  prism  in  parallel  lines :  the 
light,  having  passed  through  the  prism,  is  directed  into  a  short 
telescope  (B),  by  which  the  rays  are  again  brought  to  a  focus,  so 
that  the  image  may  be  examined  by  the  eye.  In  order  that  the 
exact  position  of  any  line  may  be  accurately  observed  and  the 
line  identified,  the  image  of  a  small  graduated  scale  illuminated 


SPECTRUM    ANALYSIS.  245 

by  a  faint  light  (C)  is  reflected  into  the  telescope  from  the  side 
of  the  prism  opposite  to  the  slit.  This  scale  corresponds  to  a 
similar  graduated  scale  which  we  might  make,  on  a  screen  on 
wh  ch  a  spectrum  is  thrown.  The  substance  of  which  the 
spectrum  is  to  be  examined  is  then  heated  on  a  platinum  wire 
in  a  Bunsen-burner  flame  exactly  opposite  the  slit.  Sometimes 
ele  :tric  sparks  are  passed  between  points  of  the  substance,  and  if 
the  latter  be  a  gas  it  must  be  enclosed  in  a  tube  and  rendered 
luminous  by  sparks  passed  through  it  from  an  induction  coil.  The 
spectra  of  most  metals  are  very  brilliant  lines  (see  frontispiece), 
so  Brilliant  that  they  entirely  obscure  the  more  faint  and  broader 
bai  ds  of  the  spectra  of  the  non-metals;  for  this  reason,  when  we 
he;  t  sodium  chloride  in  the  burner  flame,  we  can  only  observe  the 
spc  )trum  of  sodium  by  the  spectroscope,  although  the  chlorine 
mu  ,t  also  produce  its  spectrum. 

Spectroscopic  analysis  is  exceedingly  delicate:  3/oiTff, WO"  °^  a 
mil  igramme  of  sodium  chloride  introduced  into  the  burner  flame 
wil  cause  the  yellow  sodium  line  to  flash  out  for  an  instant. 
Wl  ile  studying  spectra,  several  chemists  have  observed  lines 
which  were  not  produced  by  any  substance  then  known,  and  have 
thus  been  led  to  the  discovery  of  new  elements,  of  which  small 
quantities  were  present  in  the  substances  under  examination. 

The  study  of  the  spectrum  of  the  sun's  light  and  the  light  of 
the  stars  has  shown  us  perfectly  the  elements  which  exist  in  an 
incandescent  state  in  the  atmospheres  of  those  far- distant  bodies. 
Son.e  lines  in  the  spectrum  of  sunlight  corresponded  to  those  of 
no  element  known  on  the  earth,  and  chemists  concluded  that  this 
unknown  substance  existed  in  the  sun's  atmosphere,  and  named  it 
helium.  This  same  element  has  recently  been  discovered,  by  the 
aid  of  spectrum  analysis,  in  the  lava  from  Vesuvius, — another  evi- 
dence of  the  distribution  of  the  same  elements  throughout  the 
universe,  and  of  the  unique  source  of  all  matter. 


21* 


246  LESSONS    IN   CHEMISTRY. 

LESSON    XLVIII. 
METALLIC   COMPOUNDS.— SPECIFIC   HEAT. 

408.  Before  we  undertake  the  study  of  the  individual  metals, 
we  will  pass  in  review  some  of  the  facts  which  we  have  already 
learned  concerning  metallic  compounds,  and  will  develop  them  by 
the  consideration  of  new  details. 

Oxides  and  Hydrates. — All  excepting  a  few  of  the  metals 
combine  directly  with  oxygen  at  various  temperatures.  Potassium 
is  the  only  metal  which  is  oxidized  by  bold  dry  air,  and  for  the  ox- 
idation of  some  metals  a  very  high  temperature  is  required.  The 
number  of  atomh  of  oxygen  and  of  metal  which  combine  together 
depends  on  the  atomicity  of  the  metal.  Two  atoms  of  a  mon- 
atomic  metal  combine  with  one  atom  of  oxygen,  while  in  the  for- 
mation of  a  monoxide  only  one  atom  of  a  diatomic  metal  takes 
part.  The  oxides  of  lithium,  sodium,  and  potassium  are  soluble 
in  water,  but  in  dissolving  they  form  hydrates,  which  we  must 
admit  contain  a  hydroxyl  group. 

R2Q         +         H2Q        =         2KOH 

The  hydrates  of  these  three  metals  are  the  alkaline  hydrates, 
the  metals  being  called  the  alkaline  metals.  Nearly  all  the  oxides 
are  capable,  under  certain  conditions,  of  forming  hydrates,  con- 
taining one  or  more  hydroxyl  groups,  and  the  oxidation  or  rusting 
of  metals  in  moist  air  always  results  in  the  formation  of  hydrates 
and  not  oxides.  Calcium,  strontium,  and  barium  oxides  (or  hy- 
drates) are  less  soluble  in  water  than  those  of  lithium,  sodium, 
and  potassium.  The  other  oxides  are  almost  or  entirely  insoluble 
in  water. 

Some  metals  form  several  compounds  with  oxygen,  and  those 
which  contain  the  least  oxygen  are  basic  oxides,  or  bases ;  they  are 
capable  of  reacting  with  acids,  forming  water  and  salts  in  which 
the  hydrogen  of  the  acid  is  replaced  by  metal.  Most  of  the  oxides 
containing  two  atoms  of  oxygen  also  react  with  acids,  but,  while 


OXIDES    AND    HYDRATES.  247 

water  and  a  salt  are  formed,  an  atom  of  oxygen  is  disengaged.  In 
this  manner  sulphuric  acid  liberates  ozone  from  barium  dioxide. 

3Ba02         +         3H230*        =         SBaSO*         +         O3         +         3H20 
Ba  ium  dioxide.  Barium  sulphate.  Ozone. 

The  sesquioxides,  those  containing  two  atoms  of  metal  and  three 
of  oxygen,  form  salts  which  are  important  to  understand.  Ferric 
o.\  ide  has  the  composition  Fe203 :  when  it  reacts  with  acids,  the 
t^o  atoms  of  iron  always  enter  into  one  molecule  of  the  salt 
fo  'ined.  The  vapor-density  of  ferric,  chloride  shows  that  its  mole- 
ci  le  contains  Fe2Cl6:  it  is  formed  by  the  action  of  six  molecules 
oi  hydrochloric  acid  on  one  molecule  of  ferric  oxide. 
Fe203  +  6HC1  =  FeW  +  3IPO 

\Ve  believe  that  in  ferric  oxide  and  ferric  chloride  the  atoms  of  iron  are 
te  ratoinic,  and  that  two  atoms  combine  together,  forming  a  hexatomic  couple, 
ji  st  as  two  atoms  of  carbon  are  related  in  the  hydrocarbon  C2H6.  We  may 
tb  n  contrast  the  molecular  structure  of  ferric  oxide  with  that  of  arsenious 
o>  ide  or  phosphorous  oxide  :  each  molecule  contains  three  atoms  of  oxygen  and 
tv  o  atoms  of  another  element,  but  these  atoms  are  very  differently  arranged. 

0=Fe-Fe=0 

0=As-0-As=0  0=P-0-P=0 

0 

Ferric  oxide.  Arsenious  oxide.        Phosphorus  trioxide. 

F<  rric  oxide,  then,  forms  ferric  salts  in  which  the  two  atoms  of  metal  replace 
si;:  atoms  of  hydrogen  of  the  acids.  There  are  many  other  sesquioxides  of 
th o  same  nature.  At  the  same  time  these  oxides  have  in  some  cases  the  curious 
property  of  acting  like  acid  radicals.  Ferrous  oxide,  FeO,  is  an  energetic  basic 
oxide;  it  combines  with  ferric  oxide,  and  the  combination,  Fe30*=  FeO.Fe203, 
ca  led  ferroso-ferric  oxide,  constitutes  magnetic  iron  ore,  or  black  oxide  of  iron  : 
it  is  called  a  saline,  or  salt-like  oxide. 

The  oxides  containing  one  atom  of  metal  combined  with  three 
or  more  atoms  of  oxygen  correspond  to  metallic  acids.  They  are 
capable  of  reacting  with  water  or  with  basic  oxides,  forming  well- 
marked  acids  and  salts.  Chromium  trioxide,  OO3,  corresponds  to 
chromic  acid,  H2O04  =  H20  -f  CrO3. 

When  highly  heated  with  charcoal  or  in  a  current  of  hydrogen, 
most  of  the  metallic  oxides  are  reduced  to  metal,  while  either 
carbon  monoxide,  carbon  dioxide,  or  water  is  formed.  The  oxides 
of  calcium,  barium,  strontium,  magnesium,  aluminium,  potassium, 
sodium,  and  lithium  are  not  reduced  by  hydrogen,  and  the  first 
five  are  not  reduced  by  carbon. 


248  LESSONS    IN    CHEMISTRY. 

409.  Sulphides. — Nearly  all  the  metals  combine  directly  with 
sulphur  at  certain  temperatures,  and  the  sulphides  formed  are  an- 
alogous in  composition  to  the  oxides.     The  alkaline  sulphides,  and 
those  of  calcium,  strontium,  and  barium,  are  soluble  in  water ;  the 
others  are  insoluble. 

At  temperatures  depending  upon  the  nature  of  the  metal  and 
the  state  of  division  of  the  sulphide,  oxygen  decomposes  all  the 
sulphides,  sometimes  forming  sulphur  dioxide  and  leaving  a  metal- 
lic oxide  or  even  the  free  metal,  sometimes  oxidizing  the  sulphide 
to  sulphate,  according  to  the  nature  of  the  metal.  If  a  mixture 
of  potassium  sulphate  and  powdered  charcoal  be  heated  to  redness 
in  a  covered  crucible,  a  porous  black  mass  is  obtained ;  it  contains 
potassium  sulphide,  and  if  it  be  broken  up  and  thrown  into  the 
air,  this  sulphide  is  oxidized  to  potassium  sulphate,  producing  a 
shower  of  sparks. 

R2S  +        202  K'SCM 

Potassium  sulphide.  Potassium  sulphate. 

410.  Chlorides,  Bromides,  and  Iodides. — Excepting  plati- 
num, all  the  metals  combine  directly  with  free  chlorine ;  since  in 
its  compounds  with  the  metals,  as  in  its  compound  with  hydrogen, 
chlorine  is  a  monatomic  element,  the  number  of  chlorine  atoms 
contained  in  a  molecule  of  a  metallic  chloride  is  an  indication  of 
the  atomicity  of  the  metal. 

All  the  chlorides  are  soluble  in  water,  excepting  silver  chloride, 
mercurous  chloride,  and  cuprous  chloride :  plumbic  chloride  is  only 
slightly  soluble. 

As  a  rule,  the  bromides  are  more  soluble  than  the  corresponding 
chlorides,  and  the  iodides  more  soluble  than  the  bromides. 

411.  The  color  of  the  metallic  compounds  may  be  remem- 
bered by  certain  general  principles.     If  both  the  corresponding 
oxide  or  hydrate  and  the  corresponding  acid  be  colorless,  the  salts 
are  also  colorless.     If  either  the  acid  &r  the  oxide  or  hydrate  be 
colored,  the  salts  are  colored.    The  salts  formed  by  the  same  metal 
with  colorless  acids  are  of  about  the  same  color :  with  colorless 
oxides  or  hydrates  the  same  colored   acid   forms  corresponding 
salts  of  about  the  same  color.     In  many  cases  the  color  of  metallic 


SPECIFIC    HEAT.  249 

compounds  depends  on  water  of  crystallization,  as  we  have  already 
seei.  (§  55),  and  is  lost  when  that  water  is  expelled. 

SPECIFIC    HEAT. 

4 1  2.  The  atomic  weights  of  the  inetals  cannot  often  be  estimated  from  their 
vapi  r-densities,  for  many  of  them  are  volatile  only  at  such  high  temperatures 
that  it  is  impracticable,  or  even  impossible,  to  determine  the  densities  of  their 
vaii  rs.  Some  of  the  metals  form  volatile  compounds  with  chlorine  or  with 
vari  >us  hydrocarbon  radicals;  and  since  the  molecular  weights  of  these  coin- 
pou  ids  can  be  determined  without  difficulty  from  the  densities  of  their  vapors, 
we  .  an  arrive  at  the  atomic  weight  of  the  corresponding  mejtal. 

T  le  compounds  of  the  metals  with  oxygen,  with  chlorine,  and  with  other 
bod  es  of  course  contain  a  fixed  number  of  atoms  of  metal  with  a  definite 
nun  ber  of  atoms  of  other  elements  of  which  the  atomic  weight  is  known. 
Thi  *,  we  know  that  for  every  sixteen  parts  of  oxygen,  potassium  oxide  con- 
tain i  78.2  parts  of  potassium.  We  have  already  studied  the  reasoning  by 
whi  h  we  conclude  that  the  atomic  weight  of  oxygen  is  sixteen ;  how  shall 
wo  otermine  whether  the  78.2  parts  of  potassium  represent  one,  two,  or  three 
atoi  is  of  that  metal  ? 

I  order  to  raise  the  temperatures  of  equal  weights  of  different  substances 
thr.  ugh  the  same  number  of  thermometric  degrees,  very  different  quantities 
of  1  eat  are  required.  If  we  expose  one  kilogramme  of  mercury  and  one  kilo- 
grai  ime  of  water,  both  at  0°,  to  the  same  source  of  heat,  we  find  that  when 
the  vater  will  have  been  heated  to  1°  the  mercury  will  be  at  30°.  If,  on  the 
othe-  hand,  we  place  one  kilogramme  of  mercury  at  100°,  with  some  ice,  in  a 
ves.<  :1  so  constructed  that  all  of  the  heat  will  be  employed  in  melting  the  ice, 
we  f  nd  that  only  one-thirtieth  as  much  ice  will  be  melted  as  if  we  put  in  the 
same  vessel  one  kilogramme  of  water  at  100°.  The  relative  quantities  of  heat 
which  are  required  to  raise  equal  weights  of  different  substances  through  the 
same  number  of  thermometric  degrees,  are  called  the  specific  Jieats  of  the  sub- 
stances. Water  is  the  substance  whose  specific  heat  is  chosen  as  unity,  and 
the  i-pecific  heat  of  any  substance  then  represents  the  quantity  of  heat  required 
to  raise  a  given  weight  of  the  substance  through  one  degree,  compared  with 
that  which  will  raise  the  same  weight  of  water  through  the  same  temperature. 
The  specific  heat  of  mercury  is,  then,  ^  =  0.03333.  On  comparing  the  specific 
heats  of  the  liquid  or  solid  elements,  it  has  been  found  that  just  in  the  same 
proportion  that  the  atomic  weight  increases,  the  specific  heat  diminishes ;  the 
specific  heats  are  inversely  as  the  atomic  weights.  The  product  of  the  specific 
heat  of  any  liquid  or  solid  element  by  its  atomic  weight  should,  then,  always 
give  the  same  figures.  This  important  fact  was  discovered  by  Dulong  and 
Petit,  and  is  generally  called  Duleng  and  Petit's  law :  its  import  is  evi- 
dently that  the  atoms  of  the  different  elements  all  possess  the  same  specific 
heat.  An  examination  of  the  figures  expressing  the  quantities  involved  will 
show  the  facts  on  which  the  law  is  based  : 


250 


LESSONS    IN    CHEMISTRY. 


NAME  OF  ELEMENT. 

ATOMIC  WEIGHT. 

7 

SPECIFIC  HEAT. 
0.9408 

PRODUCT. 
6.586 

Boron 

11 

0.5 

5.5 

Carbon    

...       12 

0.46 

5.52 

23 

0  2934 

6.748 

Magnesium 

...       24 

0.2499 

5.998 

...       27 

0.2143 

5.786 

31 

0  1887 

5  850 

Sulphur                       .     . 

32 

0  2026 

6  483 

Potassium   .          ... 

.     .            39  I 

0  1695 

6  500 

Zinc   

...       65  2 

0  0955 

6  230 

Bromine 

80 

0  0843 

6  744 

Iodine     
Mercury       

,     .     .     127 
...     200 

0.0541 
0.0325 

6.873 
6.494 

The  average  of  the  products  of  the  atomic  weights  by  the  specific  heats  is 
6.4  :  however,  while  the  product,  which  we  may  call  the  atomic  heat,  is  always 
near  the  number  6.4,  it  varies  within  certain  limits.  Were  it  always  6.4,  we 
could  readily  obtain  the  atomic  weight  of  any  element  by  dividing  6.4  by  the 
specific  heat;  as  it  is,  the  figures  expressing  the  specific  heat  enable  us  to 
choose  between  two  numbers  widely  separated,  and  have  in  several  cases  indi- 
cated that  the  number  which  had  been  supposed  to  represent  the  atomic 
weight  should  be  halved  or  doubled. 


LESSON    XLIX. 
LITHIUM.— SODIUM.— POTASSIUM. 

413.  Lithium,  Li  —  7. — The  metal  lithium  is  very  widely 
diffused  in  nature,  but  is  found  only  in  small  quantity,  excepting 
in  Bohemia,  where  there  are  large  mountains  of  a  peculiar  lithium 
mica,  called  lepidolite,  containing  from  three  to  six  per  cent,  of 
lithium.  Mica  is  a  silicate  of  aluminium,  potassium,  and  mag- 
nesium or  iron  ;  in  lepidolite  a  proportion  of  the  potassium  is 
replaced  by  lithium. 

Metallic  lithium  is  obtained  by  decomposing  fused  lithium  chlo- 
ride, LiCl,  a  colorless  soluble  salt,  by  a  current  of  electricity.  It 
is  a  silver-white  metal,  and  does  not  tarnish  in  dry  air.  Its  den- 
sity is  the  lowest  of  any  solid  known,  being  about  0.58.  It  melts 
at  180°,  and  may  be  melted  in  contact  with  the  air  without  be- 
coming oxidized  :  when  heated  to  redness  in  the  air  or  in  oxygen, 
it  burns  with  a  dazzling  white  flame.  Lithium  soon  becomes  tar- 


SODIUM. 


251 


nisi  ed  in  moist  air,  being  converted  into  lithium  hydrate,  LiOH  : 
when  it  is  thrown  on  the  surface  of  water,  the  same  hydrate  is 
formed,  the  water  being  decomposed  and  hydrogen  disengaged. 
The  lithium  salts  are  soluble  in  water,  and  are  colorless  unless  the 
corresponding  acid  is  colored.  They  communicate  a  red  color  to 
the  Bunsen-burner  flame,  and  their  spectrum  is  characterized  by 
a  b;  illiant  red  and  a  more  faint  orange  line  (see  frontispiece). 

•4 14.  Sodium,  Na  =  23. — Nearly  forty  per  cent,  of  the  immense 
quantities  of  sodium  chloride  existing' in  the  ocean,  in  deposits  of 
rod. -salt,  and  in  salt  wells,  consists  of  sodium.  We  have  already 
stuuied  the  processes  by  which  sodium  chloride  is  converted  into 
sod  urn  carbonate.  It  is  from  the  latter  compound  that  the  metal  is 
mai  ufactured.  The  sodium  carbonate  is  thoroughly  dried,  and 


Pio.  101. 

mixed  with  charcoal  and  enough  lime  to  prevent  the  mixture  from 
melting,  for  if  it  melted  the  charcoal  would  float  on.  the  liquid  car- 
bonate. The  mixture  is  then  heated  to  a  very  high  temperature 
in  large  cast-iron  cylinders.  Carbon  monoxide  is  disengaged,  and 
the  sodium  vapor  condenses  in  flat  receivers,  from  which  the  liquid 
metal  runs  into  vessels  containing  naphtha,  or  light  coal-oil  (Fig. 
101), 


252  LESSONS    IN   CHEMISTRY. 

Sodium  is  a  white  metal,  so  soft  that  it  can  easily  be  cut  like 
wax.  It  is  a  little  lighter  than  water,  its  density  being  0.97.  It 
melts  at  90.6°,  and  boils  at  a  red  heat.  It  can  be  melted  in  the 
air  without  taking  fire.  Its  bright  surface  rapidly  tarnishes  in 
moist  air,  being  converted  into  sodium  hydrate.  It  is  preserved  in 
bottles  containing  naphtha,  by  which  it  is  protected  from  the  air. 
When  a  small  piece  of  sodium  is  thrown  on  water,  chemical  action 
at  once  begins ;  the  sodium  melts  and  rushes  about  with  a  hissing 
noise.  The  reaction  frequently  terminates  with  an  explosion  by 
which  small  particles  of  sodium  hydrate  are  thrown  out,  and  we 
must  make  the  experiment  at  a  safe  distance  from  the  eyes.  If 
the  motion  of  the  sodium  be  arrested,  the  heat  will  accumulate 
sufficiently  to  ignite  the  escaping  hydrogen.  We 
float  a  piece  of  filter-paper  on  some  water  in  a, 
plate,  and  throw  on  this  wet  paper  a  small  piece 
of  sodium :  it  at  once  melts,  and  soon  the  hydro- 
IG>  "  gen  takes  fire,  burning  with  a  flame  tinged  bright 
yellow  by  a  little  sodium  vapor  (Fig.  102). 

415.  SODIUM  HYDRATE,  NaOH,  is  the  product  of  the  reaction 
of  sodium  with  water.  It  is  manufactured  by  a  number  of  pro- 
cesses :  when  sodium  carbonate  in  rather  dilute  solution  is  boiled 
with  milk  of  lime,  sodium  hydrate  passes  into  solution,  while  in- 
soluble calcium  carbonate  is  formed. 

Na2C03     +        Ca(OH)2        =     2NaOH     +     CaCO3 
Calcium  hydrate. 

This  operation  is  somewhat  expensive,  on  account  of  the  large 
quantity  of  water  which  must  be  boiled  away  from  the  sodium 
hydrate.  The  Le  Blanc  process  for  the  manufacture  of  sodium 
carbonate  (§  240)  can  with  slight  modifications  be  made  to  yield 
considerable  quantities  of  an  impure  sodium  hydrate,  which  re- 
mains in  solution  after  the  sodium  carbonate  has  crystallized. 

Much  sodium  hydrate  of  an  excellent  quality  is  now  manufactured  from 
cryolite  ($  240).  The  powdered  mineral  is  boiled  with  milk  of  lime,  insoluble* 
calcium  fluoride  and  a  solution  of  aluminate  of  sodium  being  obtained. 

Al2Fl6.6NaFl     +      6Ca(OH)2      =       6CaFl2      +       Al203.3Na20       +     6HaO 
Cryolite.  Calcium  hydrate.    Calcium  fluoride.    Aluminate  of  sodium. 

The  filtered  solution  is  then  boiled  with  a  new  quantity  of  pulverized  cryolite, 


SODIUM    CHLORIDE.  253 

and  all  the  sodium  is  so  converted  into  soluble  sodium  fluoride,  while  alu- 
min  urn  oxide  is  precipitated. 

Al203.3Na20     +     AlW.GNaFl     =     2A1203     +     12NaFI 


Win  n  the  insoluble  aluminium  oxide  has  settled,  the  clear  solution  of  sodium 
fluo  ide  is  drawn  off  and  boiled  with  milk  of  lime  :  calcium  fluoride  is  precip- 
itat'  d,  while  sodium  hydrate  remains  in  solution. 

2NaFl     +     Ca(OH)2     =     2NaOH     +     CaFl2 

The  aluminium  oxide  obtained  in  this  operation  is  used  for  the  manufacture 
of  a  um,  and  the  calcium  fluoride  is  employed  as  a  flux,  or  fusing  agent,  in  the 
sep;  ration  of  many  metals  from  their  ores. 

]>y  whatever  process  it  be  obtained,  the  solution  of  sodium  hy- 
dra e  is  evaporated  to  dry  ness,  and  subsequently  fused  in  iron 
boi  ers  out  of  contact  with  the  air.  It  then  forms  a  hard,  white 
soli  1,  which  if  left  exposed  to  the  air  absorbs  moisture  and  car- 
boi  dioxide,  becoming  converted  into  sodium  carbonate.  It  is 
ver  r  soluble  in  water,  and  very  caustic.  It  is  commonly  known 
as  :oncentrated  lye,  and  is  employed  in  enormous  quantities  for 
the  manufacture  of  soap. 

Hrhen  fragments  of  sodium  are  thrown  into  sodium  hydrate 
mel  ed  in  an  iron  dish,  hydrogen  is  disengaged,  and  sodium  oxide 
is  firmed. 

2NaOH     +     Na2     =     2Na20     +     H2 

416.  SODIUM  CHLORIDE,  NaCl.  —  This  compound  is  common 
salt.  It  exists  in  numerous  and  immense  deposits  of  rock-salt  in 
many  localities.  It  is  found  in  salt  wells  and  salt  springs,  and 
constitutes  the  greater  portion  of  the  solid  matter  of  sea-  water. 
The  water  of  the  Atlantic  Ocean  contains,  according  to  the  local- 
ity, from  32  to  38  grammes  of  solid  matter  per  litre  ;  the  water 
of  the  Pacific  contains  somewhat  less,  but  the  average  proportion 
of  common  salt  in  each  is  about  thirty  grammes  per  litre.  The 
other  constituents  of  sea-water  are  principally  chlorides  and  sul- 
phates of  potassium,  magnesium,  and  calcium,  with  small  quanti- 
ties of  bromides  and  iodides.  When  the  water  is  evaporated,  the 
sodium  chloride  separates  first,  while  the  other  salts  remain  in 
more  concentrated  solution.  In  warm  countries  the  evaporation 
is  often  accomplished  by  the  heat  of  the  sun  and  exposure  to  con- 

22 


254  LESSONS    IN    CHEMISTRY. 

stant  winds,  in  large  shallow  basins  into  which  the  water  is  either 
pumped  or  led  by  sluices  from  the  sea. 

Sodium  chloride  crystallizes  in  cubes,  which  may  be  obtained 
of  large  dimensions  and  perfectly  transparent,  by  the  slow  evapo- 
ration of  a  saturated  solution.  "It  is  anhydrous,  but  the  crystals, 
especially  if  small,  usually  retain  in  the  spaces  between  them  a 
small  quantity  of  water,  which  is  converted  into  steam  and  causes 
the  crystals  to  decrepitate— that  is,  crack  into  small  pieces — when 
they  are  heated.  It  is  soluble  in  less  than  three  times  its  weight 
of  cold  water,  and  in  about  two  and  a  half  times  its  weight  of 
boiling  water.  It  is  insoluble  in  pure  alcohol.  It  melts  when 
heated  to  redness,  and  volatilizes  at  a  higher  temperature. 

417.  TESTS  FOR  SODIUM. — Since  all  the  ordinary  sodium  salts 
are    soluble  and   colorless,   none    of  the  ordinary  reagents   pro- 
duce either  precipitates  or  colors  in  their  solutions.     Hydrofluo- 
silicic  acid   yields   a  white   precipitate   of  silico-sodium   fluoride 
(§  221).     We  may  readily  recognize  the  presence  of  sodium  by 
the  yellow  color  which   all  its  compounds   communicate  to  the 
colorless  flame  of  the  Bunsen  burner. 

418.  Potassium,  K  =  39. — For  a  long  time  the  principal 
source  of  potassium  was  the  potassium  carbonate  obtained  from 
wood-ashes,  and   from   that  substance  the  other  potassium  com- 
pounds were  manufactured.     Large  quantities  of  potassium  car- 
bonate are  now  obtained  from  the  double  chloride  of  potassium 
and  magnesium,  called,  from  its  source,  Stassfurth  salt  (§  242). 

Metallic  potassium  is  prepared  by  a  process  exactly  like  that 
which  yields  sodium  ;  potassium  carbonate  is  heated  with  char- 
coal ;  a  higher  temperature  is  required  than  for  the  preparation 
of  sodium.  Potassium  occurs  in  commerce  as  round,  brownish 
masses,  kept  under  naphtha  for  the  same  reason  that  sodium 
is  so  preserved.  It  is  quite  soft,  and  yields  readily  to  the  pressure 
of  the  finger-nail.  When  freshly  cut,  it  displays  a  brilliant  surface, 
but  this  rapidly  tarnishes  by  the  action  of  the  air.  Its  density  is 
about  0.86  :  it  melts  at  62.5°,  and  boils  at  a  red  heat,  emitting  a 
green  vapor.  It  combines  with  dry  oxygen,  and  in  the  cold, 
forming  potassium  oxide,  K20.  In  moist  air  it  is  converted  into 


POTASSIUM    HYDRATE. 


255 


the  hydrate  KOH.  When  a  small  piece  of  potassium  is  thrown 
in  water,  it  decomposes  the  latter  so  violently  that  the  hydrogen 
disengaged  is  at  once  ignited,  and  the  potassium  rushes  about  in 
the  burning  gas,  whose  flume  is  tinged  violet  by 
the  metal  (Fig.  103).  The  experiment  termi- 
nates with  a  little  explosion,  for  the  globule  of 
pot  issium  hydrate  formed  is  at  a  very  high  tem- 
pei  iture,  and  when  it  cools  sufficiently  to  corne 
in  -on  tact  with  the  water,  there  is  a  Budden  for- 
ma ion  of  steam. 

19.  POTASSIUM  HYDRATE,  KOH,  is  prepared  by  boiling  milk 
of  ime  with  a  rather  dilute  solution  of  potassium  carbonate.  As 
soo  i  as  the  reaction  has  terminated,  the  solution  of  potassium  hy- 
dn;  :e  is  poured  off  the  deposit  of  insoluble  calcium  carbonate,  and 
is  'apidly  evaporated  to  dry  ness  in  iron  or  silver  dishes.  It  is 
th(  u  fused,  and  cast  in  cylindrical  moulds  (Fig.  104),  so  that  it 


FIG.  103. 


FIG.  104. 

usually  occurs  in  commerce  in  round  sticks.  It  commonly  contains 
considerable  quantities  of  lime,  potassium  carbonate,  silicate,  and 
other  salts.  It  may  be  purified  by  dissolving  it  in  alcohol  in 
which  only  the  hydrate  is  soluble,  decanting  the  clear  solution, 
and.  fusing  in  a  silver  dish  the  residue  from  which  the  alcohol  has 
been  distilled.  It  is  white  and  opaque,  and  has  a  density  of  2.1. 
It  melts  at  a  red  heat,  and  volatilizes  at  a  higher  temperature.  It 


256  LESSONS    IN    CHEMISTRY. 

is  exceedingly  soluble  in  water,  and,  when  exposed  to  the  air,  ab- 
sorbs moisture  and  carbon  dioxide,  deliquescing  to  a  liquid  con- 
sisting of  a  solution  of  the  carbonate.  It  is  very  caustic  and 
corrosive,  rapidly  destroying  animal  tissues.  It  is  employed  in 
making  soft  soap. 

420.  POTASSIUM  CHLORIDE,  KC1. — This  salt  forms  transpar- 
ent, colorless  cubes,  exactly  resembling  the  crystals  of  sodium  chlo- 
ride.    It  is  found  native  in  some  localities,  and,  in  combination 
with  magnesium  chloride,  constitutes  Stassfurth  salt,  KCl,MgCl2 
-[-  6H20  (see  §  242).    It  dissolves  in  about  three  times  its  weight 
of  cold  water,  and  in  less  than  twice  its  weight  of  boiling  water. 

421.  POTASSIUM  BROMIDE,  KBr,  is  employed  extensively  in 
medicine.      It  is  usually   made  by  adding   to  bromine  enough 
strong  solution   of  potassium    hydrate  to   almost  decolorize   the 
liquid.     The  reaction  yields  a  mixture  of  potassium  bromide  and 
potassium  bromate; 

6KOH  +  3Br2  =  5KBr  +  KBrO3  +  3H20 
The  mixture  is  evaporated  to  dryness,  and  then  heated  to  red- 
ness, sometimes  with  the  addition  of  a  little  powdered  charcoal ; 
the  bromate  then  loses  its  oxygen,  and  is  converted  into  bromide. 
After  cooling,  the  mass  is  dissolved  in  water,  and  the  salt  made  to 
crystallize.  Potassium  bromide  forms  beautiful  colorless  cubes, 
having  an  intensely  salty  taste,  and  soluble  in  about  one  and  a 
half  times  their  weight  of  cold  water. 

422.  POTASSIUM  IODIDE,  KI,  is  prepared  in  exactly  the  same 
manner  as  the  biomide,  iodine  being  substituted  for  the  bromine. 
It  also  crystallizes  in  colorless  cubes  having  a  salty  and  at  the 
same   time   bitter   taste.      It   dissolves    in   about    two-thirds   its 
weight  of  cold  water,  and  the  solution  will  dissolve  large  quanti- 
ties of  iodine,  becoming  dark  brown  in  color.     Both  the  bromide 
and   iodide  of  potassium  of  commerce  occur  not  in  transparent 
but  in  white,  opaque  crystals :  they  contain  a  trace  of  free  alkali. 
When  the  transparent  crystals  have  been  put  in  the  market,  they 
have  found  no  sale,  being  supposed  to  be  impure. 

423.  TESTS  FOR  POTASSIUM. — Like  the  salts  of  sodium,  most 
of  the  potassium  salts  are  colorless  and  soluble,  and  their  solutions 


SILVER.  257 

arc  neither  precipitated  nor  colored  by  the  ordinary  reagents. 
Hydrofluosilicic  acid  produces  a  gelatinous  white  precipitate  of 
sili co-potassium  fluoride.  When  the  solution  of  a  potassium  salt 
is  mixed  with  a  strong  solution  of  tartaric  acid,  a  white  crystal- 
lin-3  precipitate  of  cream  of  tartar  soon  separates.  Platinic  chloride, 
PtOl4,  produces  a  yellow,  crystalline  precipitate  of  potassio-plutinic 
ch  oride,  (KCl)2PtCl4.  The  potassium  compounds  impart  a  violet 
co  )r  to  flame,  but  the  color  is  rather  delicate,  and  often  masked 
b}  the  presence  of  sodium  or  lithium:  it  is  then  examined  through 
a  1  'lue  glass  which  does  not  allow  the  passage  of  the  light  from 
th  sodium  and  lithium  flames,  but  through  which  the  violet 
po  assium  flame  is  distinctly  visible. 

24.  Analogies  of  Lithium,  Sodium,  and  Potassium. — When  we  compare 
tou  ither  the  compounds  of  the  metals  which  we  have  just  studied,  we  find 
th:  t  the  three  form  a  group  presenting  the  most  evident  chemical  analogies. 
Th  -y  are  monatomic  metals,  capable  of  replacing  the  hydrogen  of  acids,  atom 
for  atom.  One  atom  of  either  metal  will  combine  with  one  atom  of  chlorine, 
or  vith  one  hydroxyl  group,  but  two  atoms  are  required  to  combine  with  the 
di:i  ;omic  atom  of  oxygen.  Moreover,  the  corresponding  salts  of  these  metals 
an  isomorphous:  they  crystallize  either  in  exactly  the  same  forms,  or  in  forms 
wl;  ch  are  easily  derived  one  from  the  other.  The  rare  metals  caesium  and 
rul  idium  form  part  of  the  group  just  considered. 


LESSON    L. 

SILVER.     Ag  =  1 08. 

425.  Silver  is  found  in  the  metallic  state,  and  in  combination 
with  many  other  elements,  among  the  more  ordinary  of  which  are 
sulohur,  chlorine,  arsenic,  antimony,  and  lead. 

When  the  silver  ores  do  not  contain  lead,  the  silver  is  extracted 
by  amalgamating  it  with  mercury  and  then  driving  off  the  latter 
by  the  action  of  heat.  Several  processes  are  employed ;  in  all  of 
them  the  silver  is  first  converted  into  silver  chloride.  The  German 
method  consists  in  roasting  the  powdered  ore  with  common  salt : 
the  sulphides  present  are  thus  oxidized,  while  the  silver  is  con- 
verted into  chloride.  The  cold  mass  is  pulverized,  and  washed 
r  22* 


258  LESSONS   IN    CHEMISTRY. 

with  water  to  remove  all  soluble  salts  formed ;  the  residue  is  then 
put  into  barrels  with  water  and  scrap  iron,  and  these  amalgamation 

barrels  are  rotated  by  machinery 
until  the  contents  are  thoroughly 
mixed  (Fig.  105).  Silver  is  set 
free,  while  the  chlorine  combines 
with  the  iron.  Mercury  is  now 
introduced,  and  forms  an  amalgam 
with  the  silver.  The  liquid  amal- 
gam is  strongly  pressed  in  canvas 
bags,  and  the  greater  part  of  the 
j,  JQK  *  mercury  is  squeezed  out.  The 

semi-solid  amalgam  remaining  is 
heated  until  the  mercury  is  expelled,  and  the  residue  is  metallic 
silver  containing  a  certain  proportion  of  copper  derived  from  copper 
sulphide  in  the  ore. 

In  the  process  adopted  on  the  Pacific  slope,  the  ore  is  reduced 
to  a  very  fine  powder,  which  is  mixed  with  a  proportion  of  com- 
mon salt  depending  on  the  amount  of  silver  to  be  chloridized. 
By  appropriate  machinery,  this  mixture  is  thrown  into  a  tall 
chimney-shaft  through  which  a  current  of  very  hot  air  is  rising. 
Under  these  circumstances,  all  the  silver  is  at  once  converted  into 
chloride,  which  falls  to  the  bottom  of  the  shaft,  from  which  it  is 
removed  when  about  a  ton  has  accumulated.  It  is  then  washed 
in  a  stream  of  water,  and  the  insoluble  silver  chloride  settles  as 
a  pulpy  mass.  This  pulp  is  mixed  with  a  little  cupric  sulphate 
and  common  salt  in  iron  pans  heated  by  steam,  and  about  one 
hundred  and  fifty  pounds  of  mercury  are  added  for  every  ton  of 
the  pulp.  After  five  or  six  hours'  grinding,  the  mercury  contains 
all  the  silver,  which  is  reduced  partly  by  the  iron  of  the  pan, 
partly  by  the  conversion  of  some  mercury  into  chloride.  The 
amalgam  is  then  agitated  with  water,  and,  after  it  is  dried,  the 
mercury  is  driven  off  by  distillation  in  cast-iron  retorts. 

426.  Galena,  or  lead  sulphide,  an  important  lead  ore,  often  con- 
tains a  considerable  proportion  of  silver,  which  forms  an  alloy  with 
the  lead  when  the  ore  is  reduced.  Large  quantities  of  silver  are 


SILVER. 


259 


extracted  from  such  lead  by  a  process  called,  from  the  name  of  its 
inventor,  Pattinsonizing.  When  a  melted  alloy  of  lead  and  sil- 
ver containing  even  small  quantities  of  the  latter  metal  is  allowed 
to  ;ool,  almost  pure  lead  first  solidifies  in  crystals  ;  this  is  the  fact 
on  which  the  process  is  based.  The  molten  lead  is  allowed  to 
coi  1  slowly,  and,  by  means  of  large  ladles,  the  crystals  of  lead  are 
rei  loved  as  fast  as  they  are  formed,  so  that  the  metal  which 
rei  lains  liquid  to  the  last  is  an  alloy  rich  in  silver  (Fig.  106). 


FIG.  106. 

As  the  lead  crystals  so  removed  still  contain  a  little  silver,  they 
are  submitted  a  second  and  a  third  time  to  the  same,  operation,  so 
that  pure  lead  is  obtained  on  one  hand,  and  a  very  rich  silver  alloy 
on  the  other.  The  lead  is  entirely  removed  from  the  alloy  by 
a  process  called  cupellation.  The  metal  is  melted  on  a  shallow 
hearth  swept  by  the  flame  of  a  small  furnace.  This  hearth,  which 


260 


LESSONS    IN    CHEMISTRY. 


is  called  a  cupel,  is  covered  by  a  sheet-iron  dome  (Gr,  Fig.  107), 
which  can  be  raised  and  lowered  as  necessary.     When  the  whole 


FIG.  107. 

of  the  metal  is  melted,  a  blast  of  air  is  blown  on  its  surface  from 
pipes  called  tuyeres  (t  £),  and  the  lead  is  oxidized.  The  oxide 
melts,  and,  being  lighter  than  the  metal,  is  drawn  off  through  a 
notch  cut  in  the  side  of  the  cupel,  and  the  notch  is  gradually 
deepened  as  the  level  of  the  fused  metal  becomes  lowered.  The 
silver  does  not  oxidize,  and  at  last,  when  its  surface  is  covered  with 
only  a  thin  layer  of  molten  lead  oxide,  that  layer  breaks  suddenly, 
and  the  brilliant  surface  of  the  silver  appears  with  a  flash.  The 
blast  of  air  is  then  stopped,  and  the  silver  is  either  drawn  off  into 
ingot-moulds  or  allowed  to  solidify  in  the  cupel. 

427.  Silver  is  the  most  brilliantly  white  metal.  It  is  exceed- 
ingly malleable  and  ductile.  Its  density  is  10.5.  It  does  not 
tarnish  on  exposure  to  the  air,  but  above  its  melting  point,  which 
is  about  1000°,  it  absorbs  or  combines  with  about  twenty-two  times 
its  volume  of  oxygen  from  the  air.  The  oxygen  is  expelled  vio- 
lently as  the  metal  solidifies,  and  portions  of  the  still  liquid  silver 
are  often  projected  from  the  vessel,  while  its  surface  is  thrown  into 
curious  tree-like  forms.  This  phenomenon  is  called  spitting. 


SILVER    CHLORIDE    AND    OXIDE.  261 

Ozone  oxidizes  silver  to  the  dioxide  Ag2O2.  It  is  blackened  by 
hydrogen  sulphide,  silver  sulphide  being  formed  on  its  surface ; 
the  discoloration  of  silver-ware  is  due  to  traces  of  hydrogen  sul- 
phi  le  in  the  air ;  the  sulphur  in  eggs,  mustard,  etc.,  rapidly 
blat  kens  silver  spoons.  Boiling  sulphuric  acid  dissolves  silver 
slovly,  converting  it  into  sulphate ;  hydrochloric  acid  forms  in- 
soli  ble  silver  chloride  on  its  surface,  and  the  metal  beneath  is  so 
pro  ected  from  further  action.  It  dissolves  readily  in  nitric  acid, 
red  vapors  being  disengaged  and  silver  nitrate  formed.  It  is  not 
att;  eked  by  the  alkaline  hydrates,  and  therefore  silver  vessels  are 
use  1  for  the  concentration  and  fusion  of  those  compounds. 

-28.  SILVER  CHLORIDE,  AgCl,  is  one  of  the  more  important 
sihur  ores;  it  is  the  mineral  horn-silver,  so  called  from  its  ap- 
per,  ranee  and  somewhat  elastic,  horn-like  structure.  We  have 
aln  ady  seen  that  it  is  precipitated  on  the  addition  of  hydrochloric 
aci  [  or  a  soluble  chloride  to  solution  of  silver  nitrate.  It  then 
for  us  a  white,  curdy  precipitate,  which  darkens  and  undergoes 
par  ial  decomposition  on  exposure  to  light.  If  a  piece  of  zinc  be 
pla  :ed  in  some  recently -precipitated  and  still  moist  silver  chloride, 
the  whole  of  the  silver  soon  separates  in  the  form  of  a  gray 
powder,  while  zinc  chloride  is  formed.  Pure  silver  may  be  thus 
obt  lined,  but  for  that  purpose  the  silver  chloride  should  be  pre- 
viously well  washed  with  dilute  sulphuric  acid,  and  the  silver 
powder  must  be  thoroughly  washed  by  shaking  it  many  times 
witii  water  and  then  allowing  it  to  settle.  Pure  silver  may  also 
be  made  by  fusing  the  well-washed  chloride  with  sodium  carbon- 
ate ;  carbon  dioxide  and  oxygen  are  disengaged,  sodium  chloride 
is  formed,  and  the  silver  remains  as  a  button  at  the  bottom  of  the 
crucible.  When  recently  precipitated,  silver  chloride  dissolves 
readily  in  ammonia-water,  from  which  it  is  again  deposited  when 
the  ammonia  is  neutralized  by  an  acid. 

429.  SILVER  OXIDE,  Ag20,  is  made  either  by  precipitating  a 
solution  of  silver  nitrate  by  potassium  hydrate,  or  by  boiling 
well-washed  silver  chloride  with  potassium  or  sodium  hydrate  so- 
lution. It  is  a  brown  powder,  insoluble  in  water,  and  decomposed 
by  heat  into  silver  and  oxygen. 


262  LESSONS    IN    CHEMISTRY. 

430.  SILVER  SULPHIDE,  Ag2S,  is  found  native  in  small  octa- 
hedral crystals.     It  is  precipitated  by  the  action  of  hydrogen  sul- 
phide on  solution  of  silver  nitrate,  and  may  be  formed  by  the  direct 
union  of  silver  and  sulphur  at  a  slightly-elevated  temperature. 

431.  TESTS  FOR  SILVER. — In  solutions  of  silver  salts,  hydro- 
chloric acid  produces  a  white  precipitate  of  silver  chloride ;  this 
precipitate  is  soluble  in  ammonia-water,  and  darkens  in  color  when 
exposed  to  light.     Potassium  iodide  solution  gives  a  yellow  pre- 
cipitate of  silver  iodide,  Agl,  which  also  darkens  by  the  action  of 
light,  but  is  only  slightly  soluble  in  ammonia.    Hydrogen  sulphide 
precipitates  black  silver  sulphide.    Potassium  chromate  precipitates 
red  silver  chromate,  Ag'2O04,  in  neutral  solutions  which  are  not 
too  dilute. 

432.  SILVER-PLATING. — It  is  often  desired  to  cover  other  inetals  or  glass 
with  a  thin  layer  of  silver.     This  may  be  accomplished  in  several  manners. 
Copper  objects   may  be  silvered  by  rubbing  them  with  a  mixture  of  moist 
silver  chloride  and  sodium  carbonate,  but  the  layer  of  silver  so  deposited  is 
very  thin.     The  metals  are  most  readily  and  evenly  silvered  by  connecting 
the  object  to  be  plated  with  the  zinc  pole  of  a  voltaic  battery  and  immersing 
it  in  a  solution  of  silver  and  potassium  double  cyanide,  made  by  boiling  silver 
chloride  in  a  solution  of  potassium  cyanide.     The  positive  pole  of  the  battery 
is  connected  with  a  plate  of  silver,  or  silver  coin,  immersed  in  the  same  liquid. 
The  silver  solution  then  always  retains  its  strength,  for  the  metal  dissolving 
from  the  positive  electrode  replaces  that  which  is  deposited  on  the  article  to 
be  silvered.     We  may  readily  coat  the  interior  of  a  test-tube  with  a  thin  layer 
of  silver  by  pouring  into  it  a  solution  of  silver  nitrate  and  sufficient  ammonia- 
water  to  redissolve  the  precipitate  first  formed  :  we  then  add  a  few  drops  of  a 
solution  of  tartaric  acid,  and  place  the  tube  in  water  heated  to  about  50°.     A 
flat  piece  of  glass  may  be  silvered  by  the  same  liquid,  which  is  then  poured 
on  in  just  sufficient  quantity  to  cover  evenly  the  perfectly-cleaned  glass.    The 
layer  of  silver  so  formed  is  very  thin,  and  allows  the  passage  of  a  violet  light. 
It  is  protected  from  accident  by  a  coat  of  paint. 

433.  ASSAYING  OP  SILVER. — The  term  assaying  means  determining  the  pro- 

portion of  pure  metal  in  either  an  alloy  or  an  ore,  but 
is  now  usually  restricted  to  the  first.  Silver  is  alloyed 
with  copper,  and  the  alloy  may  be  assayed  either  by  a 
dry  process — that  is,  one  in  which  no  liquid  is  employed 
— or  by  a  wet  process.  The  dry  process  consists  in  melt- 
FlG.  108.  ing  a  small  quantity  of  lead  in  a  cupel,  which  is  a  little 

shallow  cup  made  of  compressed  bone-ash  and  is  very 

porous  (Fig.  108).    A  weighed  quantity  of  the  silver  coin  or  jewelry  to  be  as- 
sayed is  then  wrapped  in  a  small  piece  of  paper  and  placed  on  the  surface  of 


SILVER    ASSAY. 


263 


the  melted  lead,  in  which  it  is  quickly  dissolved.  The  cupel  is  heated  in  a 
rnuflle  (A,  Fig.  109)  which  fits  into  an  opening  in  the  side  of  a  muffle-furnace. 
The  muffle  is  open  only  at  the  exterior  end,  and  has  a  slit  in  the  arched  top, 
so  th  it  the  air  is  drawn  through  it  by  the  draught  of  the  furnace.  The  lead  is 
oxid  zed  by  the  air,  and  in  presence  of  lead  the  copper  of  the  alloy  becomes 
also  'onverted  into  oxide ;  the  fused  oxides  are  absorbed  by  the  porous  cupel, 
and  is  soon  as  their  last  traces  disappear,  the  flashing  of  the  bright  silver 
surf;  oe  indicates  that  the  operation  is  finished.  When  cold,  the  button  of 
pure  silver  is  weighed. 

Tl  e  wet  assay  is  an  example  of  volumetric  analysis  which  we  must  study. 
We  enow  that  by  the  addition  of  a  solution,  of  common  salt  to  one  of  silver 
nitr;  te,  silver  chloride  is  precipitated,  and,  since  one  molecule  of  sodium  chlo- 
ride 'eacts  with  one  molecule  of  silver  nitrate,  we  find  that  58.5  parts  by  weight 
of  s  ilt  will  precipitate  exactly  108  parts  of  silver  in  the  form  of  chloride. 

NaCl         +         AgXQS         -         AgCl         +         NaNO3 
(23  +  35.5)  (108  +  14  +  48)  (108+35.5)  (23  +  14+48) 

By  >  irefully  adding  a  solution  of  common  salt  to  a  solution  of  silver  nitrate, 
we  c  in  tell  when  all  the  silver  has  been  converted  into  chloride,  for  no  more 
precipitate  is  then  formed.  Now,  if  we  know 
how  much  salt  we  have  added,  we  can  easily 
calculate  how  much  silver  was  pres- 
ent, because  every  58.5  parts  of  salt 
used  will  represent  108  parts  of  silver 
precipitated.  Let  us  make  a  solu- 
tion of  salt  of  which  each  litre  shall 
precipitate  ten  grammes  of  silver. 
Since  108  grammes  of  silver  require 
58.5  grammes  of  salt,  10  grammes  of 


silver  will   require   58:5  X  10  =  5.417 
108 


grammes  of  salt.  We  make  such  a 
solution,  and  we  know  that  every 
cubic  centimetre  of  it  will  precip- 

itate  1Qgrammes  =  1  centigramme  of 
1000 

silver.      We  now    dissolve    in    nitric 
acid  about  a  gramme  of  our  alloy  of 
silver,  accurately  weighed,  and  then      mS 
introduce    our    salt    solution    into    a 
FIG.  109.  burette  (Fig.  110),  which  is  a  glass  FIG.  110. 

tube  having  a  stop-cock  at  the  bot- 
tom, and  graduated  so  that  we  may  measure  how  much  of  the  liquid  we  allow 
to  run  out.    Then  the  salt  solution  is  slowly  dropped  into  the  solution  of  silver 
nitrate,  which  is  agitated  so  that  the  precipitate  may  quickly  settle,  until  the 
instant  arrives  when  a  drop  produces  no  precipitate.     We  then  carefully  read 


264  LESSONS    IN    CHEMISTRY. 

off  the  exact  quantity  of  salt  solution  used,  and  calculate  the  amount  of  silver 
present  in  the  quantity  of  alloy  analyzed,  each  cubic  centimetre  of  the  salt 
solution  representing  0.01  gramme  of  silver. 

The  silver  coins  of  the  United  States  contain  90  per  cent,  of  silver  and  10 
per  cent,  of  copper. 

434.  PHOTOGRAPHY. — The  chloride,  bromide,  and  iodide  of 
silver,  being  partially  decomposed  by  the  action  of  light,  are  em- 
ployed in  photography.  An  image  of  the  object  to  be  photo- 
graphed being  thrown  on  a  glass  plate  coated  with  either  of  these 
sensitive  salts,  those  portions  on  which  the  light  falls  are  dark- 
ened, and  metallic  silver  is  formed ;  the  shades  or  dark  parts  of 
the  image  remain  unaffected  in  proportion  to  the  intensity  of  the 
shade :  then  when  the  plate  is  placed  in  a  liquid  capable  of  dis- 
solving the  unaltered  salts,  a  negative  photograph  is  obtained;  that 
is,  one  in  which  the  natural  lights  and  shades  are  reversed.  This 
negative  being  placed  over  a  paper  sensitized  by  some  compound 
alterable  by  light,  a  positive  picture  is  obtained,  for  the  light  acts 
through  the  transparent  portions  of  the  negative.  We  can  easily 
make  a  sensitive  paper  by  soaking  a  piece  of  soft  white  paper  in 
a  solution  of  common  salt,  and,  after  drying  it,  putting  it  in  a 
solution  of  silver  nitrate  in  a  dark  room.  Silver  chloride  is  thus 
formed  in  the  paper.  If  now  we  have  a  negative  or  drawing  on 
glass,  we  may  make  a  photograph  ;  or  we  may  copv  some  leaves 
by  placing  them  on  the  paper,  and,  after  pressing  them  down  un- 
der a  glass  plate,  expose  the  whole  to  the  action  of  sunlight.  In 
a  quarter  of  an  hour  we  remove  the  plate,  and  soak  the  paper  in 
a  solution  of  sodium  thiosulphate  (§  106),  which  dissolves  out  the 
unaltered  silver  chloride :  this  is  necessary,  since  the  light  would 
otherwise  blacken  the  paper  uniformly.  After  thoroughly  wash- 
ing the  paper  in  water,  we  have  an  exact  copy  of  the  negative  or 
leaves  employed. 


CALCIUM.  265 

LESSON    LI. 
CALCIUM.— STRONTIUM.— BARIUM. 

1  35.  These  three  elements  form  a  group  of  metals  of  which  the  correspond- 
in"  compounds  not  only  present  remarkable  chemical  analogies,  but  resemble 
on<  another  in  many  physical  properties.  We  have  already  had  occasion  to 
not  ce,  during  the  study  of  certain  of  their  salts,  that  they  are  diatomic  ele- 
ments, capable  of  replacing  two  atoms  of  hydrogen  in  the  acids. 

ri  he  metals  are  obtained  by  decomposing  their  fused  chlorides  by  a  power- 
ful electric  current.  They  are  harder  than  lead,  and  their  surfaces,  which  are 
bri  liant  when  freshly  filed,  rapidly  tarnish  in  moist  air.  They  decompose 
col  I  water,  forming  hydrates  while  hydrogen  is  disengaged;  when  heated  in 
tin  air  or  in  oxygen,  they  take  fire  and  burn  brilliantly. 

136.  Calcium,  Ca  =  40,  is  the  metallic  radical  of  lime,  marble, 
g}  3sum,  etc.     Its  density  is  about  1.6. 

137.  CALCIUM  CHLORIDE,  CaCl2,  may  be  made  by  dissolving 
wl  ite  marble  in  hydrochloric  acid.     It  is  now  obtained  in  large 
qmntities  as  an  accessory  product  in  the  manufacture  of  sodium 
carbonate  by  the  ammonia  process.     It  crystallizes  in  large  color- 
less prisms  containing  six  molecules  of  water  of  crystallization. 
These  crystals  are  deliquescent;  when  they  dissolve  in  water,  in 
winch  they  are  very  soluble,  they  produce  a  marked  lowering  of 
temperature.     A  mixture  of  equal  weights  of  crystallized  calcium 
chloride  and  snow  or  broken  ice  produces  a  temperature  of — 45°. 
When  heated,  the  crystals  melt,  and  at  200°  four  molecules  of 
water  are  driven  out,  but  the  other  twr>  are  retained  until  the 
temperature  reaches  redness.     As  the  anhydrous  calcium  chloride 
cools,  it  then  solidifies  to  a  hard,  white,  crystalline  mass ;  this  is 
used  for  drying  gases  and  liquids  with  which    it   undergoes   no 
chemical  reaction.     Its  solution  in  water  develops   considerable 
heat. 

A  saturated  solution  of  calcium  chloride  boils  at  179.5°.     The 
low  cost  of  calcium  chloride  obtained  in  the  ammonia-soda  pro- 
cess has  permitted  the  adoption  of  a  new  and  very  cheap  process 
for  the  extraction  of  sulphur  from  the  earthy  matters  with  which 
M  23 


266 


LESSONS     IN     CHEMISTRY. 


it  occurs.  The  sulphur  ore  is  immersed  in  a  hot  solution  of  cal- 
cium chloride  of  such  strength  that  it  boils  at  about  120°  ;  the 
sulphur  then  melts  and  runs  out  of  the  earthy  matters,  and  may 
be  drawn  off  as  it  collects  below  the  hot  liquid. 

438.  CALCIUM  OXIDE,  CaO. — This  substance  is  universally 
known,  and  commonly  called  lime.  It  is  manufactured  by  de- 
composing limestone,  which  is  calcium  carbonate,  by  the  action 
of  heat,  but  it  is  necessary  that  the  products  of  combustion  shall 
pass  through  the  heated  mineral,  for  calcium  carbonate  is  decom- 
posed only  at  exceedingly  high  temperatures  when  heated  in  cov- 
ered vessels.  Very  primitive  furnaces  or  lime-kilns  are  usually 
employed,  resembling  holes  in  the  side  of  a  hill :  above  an  open- 
ing at  the  bottom  a  sort  of  grate  is  arranged,  and  on  this  the  coal 
and  limestone  are  thrown  from  the  top.  The  tire  is  then  lighted, 
and  in  about  three  days  the  kiln  is  burned  out.  A  continuous 


FIG.  111. 

and  more  economical  lime-kiln  has  an  opening  at  the  base  for  the 
removal  of  the  lime,  and  about  three  metres  above  this  opening 
there  are  others  by  which  the  flames  from  furnaces  pass  directly 
into  the  mass  of  limestone.  As  the  lime  is  raked  out  at  the  bot- 
tom, the  limestone  descends,  and  more  is  thrown  in  at  the  top 
(Fig.  111). 


LIME.  267 

Lime  occurs  in  hard,  compact  masses  of  a  white  or  gray  color  : 
it  is  called  quick-lime.  It  is  infusible  at  the  highest  temperatures 
which  we  can  produce.  When  exposed  to  the  air,  it  absorbs 
moisture  and  carbon  dioxide,  cracks,  increases  in  volume,  and 
crumbles  to  a  white  powder,  which  consists  of  a  mixture  of  cal- 
cium hydrate  and  calcium  carbonate.  When  a  mass  of  lime  is 
sprinkled  with  water,  the  latter  is  absorbed ;  in  a  short  time  the 
lin  e  becomes  so  hot  that  steam  is  given  off,  and,  if  sufficient 
water  be  used,  the  whole  falls  to  a  bulky  powder  of  calcium  hy- 
dr,  te,  Ca(OH)2,  which  is  called  slaked  lime.  Lime  which  de- 
ve  ops  much  heat  and  increases  greatly  in  volume  by  hydration 
is  called  fat  lime,  but  if  there  be  little  heat  produced,  and  the 
vo  ume  not  greatly  augmented,  the  lime  is  said  to  be  poor  lime  ; 
it  then  contains  considerable  quantities  of  magnesia,  silica,  and 
cl;  y,  derived  from  a  poor  quality  of  limestone.  When  such  lime 
is  ;oo  highly  heated  during  the  burning,  calcium  silicate  is  formed 
in  hard,  semi-fused  masses,  and  the  lime  is  said  to  be  overburnt. 

Milk  of  lime  is  calcium  hydrate,  that  is,  slaked  lime,  suspended 
in  water.  If  this  white,  creamy  liquid  be  allowed  to  settle,  the 
clear  liquid  obtained  is  lime-water.  It  is  a  solution  of  calcium 
hy  Irate,  which  dissolves  in  about  seven  hundred  times  its  weight 
of  cold  water.  It  is  only  about  half  as  soluble  in  boiling  water. 
When  lime-water  is  heated,  it  becomes  turbid  from  the  separa- 
tion of  part  of  the  hydrate,  which  again  dissolves  as  the  liquid  cools. 

Large  quantities  of  lime  are  employed  in  building  operations. 
Ordinary  mortar  is  a  mixture  of  slaked  lime  and  sand,  the  prin- 
cipal object  of  the  latter  being  to  prevent  the  shrinking  of  the 
mortar  as  it  dries.  Mortar  hardens  because  the  calcium  hydrate 
gradually  absorbs  carbon  dioxide  from  the  air,  and  the  calcium 
carbonate  formed,  adhering  strongly  to  the  surfaces  with  which  it 
is  in  contact,  binds  them  together.  It  is  possible  that  a  small 
proportion  of  calcium  silicate  is  also  formed  during  the  hard- 
ening. 

Cements,  of  which  Portland  cement*  is  an  excellent  type,  are 


*  Named  from  its  resemblance  to  Portland  stone. 


268 


LESSONS   IN   CHEMISTRY. 


made  by  calcining  limestone  with  from  ten  to  thirty  per  cent,  of 
clay.  Sometimes  the  clay  exists  naturally  in  the  limestone;  some- 
times it  is  added  in  the  form  of  dried  river-mud.  Clay  is  a  hy- 
drated  aluminium  silicate,  and  is  rendered  anhydrous  by  the  action 
of  heat.  It  is  probable  that  at  the  same  time  a  little  calcium  sili- 
cate and  aluminate  of  calcium  are  formed.  However  that  may  be, 
the  hard  mass  resulting  from  the  calcination  is  pulverized,  and 
the  powder  is  cement,  or  hydraulic  lime.  When  it  is  mixed  with 
water,  it  sets,  or  hardens  to  a  solid  mass,  in  a  very  short  time.  It 
has  the  property  of  hardening  under  water,  and  is  invaluable  in 
submarine  architecture.  Its  hardening  is  apparently  due  to  the 
formation  of  a  double  silicate  of  aluminium  and  calcium. 

439.  CHLORINATED  LIME,  CaCl(ClO). — This  compound,  which 


FIG.  112. 

is  intermediate  between  calcium  chloride,  CaCl2,  and  calcium  hy 
pochlorite.  Ca(ClO)2,  is  manufactured  on  an  extensive  scale  by 
passing  chlorine  gas  over  well-slaked  lime  placed  in  thin  layers 
on  shelves  in  masonry  chambers  (Fig.  112),  care  being  taken  that 
the  temperature  does  not  become  too  elevated.  It  is  largely  em- 


STRONTIUM.  269 

ployed  as  a  bleaching  and  disinfecting  agent,  and  owes  this  prop- 
erty to  the  facility  with  which  it  gives  up  its  chlorine.  It  is 
dt  composed  by  very  dilute  acids,  even  by  the  carbon  dioxide  of 
the  air. 

CaCl(ClO)         +        CO2        =        CaCO3        +        Cl« 

When  thrown  into  water,  it  yields  a  solution  containing  calcium 
h  pochlorite  and  calcium  chloride. 

2CaCl(C10)         =         CaCl2.         +         Ca(ClO)2 
Chlorinated  lime.  Calcium  hypochlorite. 

When  it  is  heated,  or  when  its  solution  is  boiled,  it  is  converted 
into  calcium  chloride  and  calcium  chlorate. 

6CaCl(C10)         =         5CaCl2         +         Ca(C103)2 
Chlorinated  lime.  Calcium  chlorate. 

440.  TESTS  FOR  CALCIUM. — Solutions  of  calcium  salts  are  not 
afected  by  hydrogen  sulphide.     In  solutions  which  are  not  very 
di.ute,  sulphuric  acid  and  the  soluble  sulphates  produce  a  white 
pi  ecipitate  of  calcium  sulphate.     Solution  of  oxalic  acid  to  which 
a  ?ew  drops  of  ammonia  have  been  added,  yields  a  white  precipitate 
of  calcium  oxalate,  even  in  the  most  dilute  calcium  solutions.    The 
sa.ts  of  calcium  communicate  a  reddish-yellow  color  to  flame,  and 
th  3  calcium  spectrum  is  quite  characteristic.  (See  frontispiece.) 

441.  Strontium,  Sr  =  87.5. — The  principal  strontium  minerals 
an;  the  sulphate,  called  celestine,  on  account  of  the  blue  color  of 
muny  specimens,  and  the  carbonate,  called  strontianite.     The  first, 
being  the  more  abundant,  serves  for  the  preparation  of  the  stron- 
tium salts :   it  is  powdered,  and  intimately  mixed  with  charcoal, 
and  the  mixture  heated  to  bright  redness  in  a  covered  crucible. 
Carbon  monoxide  is  then   disengaged,  while  the  sulphate  is  re- 
duced to  the  sulphide,  SrS.     The  gray  mass  containing  this  sul- 
phide is  then  treated  with  the  acid  corresponding  to  the  desired 
salt,  which  separates  in  crystals  when  the  solution  is  evaporated. 

442.  STRONTIUM  CHLORIDE,  SrCl2,  is  made  by  dissolving  the 
sulphide  in  hydrochloric  acid  and  evaporating  the  filtered  solution. 
It  crystallizes  in  deliquescent  needles  containing  three  molecules 
of  water  of  crystallization  for  one  molecule  of  the  salt.    It  is  very 

23* 


270  LESSONS    IN    CHEMISTRY. 

soluble  in  water,  and  slightly  soluble  in  alcohol,  the  latter  solution 
burning  with  a  red  flame. 

443.  STRONTIUM    MONOXIDE,  SrO,  is  prepared    by  strongly 
calcining  strontium  nitrate  obtained  by  dissolving  the  sulphide  in 
nitric  acid.     It  is  an  infusible,  gray,  porous  mass :  when  exposed 
to  the  air,  it  absorbs  moisture  and  carbon  dioxide.     By  the  action 
of  water,  it  is  converted  into  strontium  hydrate,  Sr(OH)2,  which 
is  soluble  in  about  fifty  times  its  weight  of  cold  or  two  and  a  half 
times  its  weight  of  boiling  water,  and  may  be  obtained  in  crystals 
with  eight  molecules  of  water  of  crystallization. 

444.  STRONTIUM  DIOXIDE,  SrO2,  is  formed  by  the  action  of 
oxygen  on  the  monoxide  at  a  dull  red  heat. 

445.  TESTS  FOR  STRONTIUM. — Solutions  of  the  ordinary  salts 
of  strontium  are  colorless ;  they  are  not  precipitated  by  hydrogen 
sulphide.     Sodium  carbonate  produces  a  voluminous  white  precip- 
itate of  strontium  carbonate.     Sulphuric  acid  precipitates  stron- 
tium sulphate  in  solutions  which  are  .not  too  dilute.     Oxalic  acid 
and  ammonia  produce  a  white  precipitate  of  strontium  oxalate. 
Flame  is  colored  red  by  strontium  compounds. 

446.  Barium,  Ba  — 137. — Barium  occurs  in  nature  in  heavy- 
spar,  which  is  the  sulphate,  and  witherite,  which  is  the  carbonate. 
Its  salts  may  be  prepared  by  dissolving  the  native  carbonate  in 
the  corresponding  acid,  or  from  the  sulphate,  which  must  first  be 
reduced  to  sulphide.     The  finely-powdered  sulphate  is  made  into 
a  paste  with  rosin  and  linseed  oil,  and  the  mixture  is  shaped  into 
little  balls  which  are  calcined  in  a  covered  crucible. 

447.  BARIUM  CHLORIDE,  BaCl2,  is  obtained  when  the  sulphide 
is  dissolved  in  hydrochloric  acid,  and  the  filtered  solution  suffi- 
ciently concentrated.     Its  crystals  contain  two  molecules  of  water. 
They  are  soluble  in  rather  more  than  twice  their  weight  of  cold 
water,  in  much  less  boiling  water,  and   also  slightly  soluble  in 
alcohol.     Barium  chloride  is  the  reagent  generally  used  for  the 
detection  of  sulphuric  acid. 

448.  BARIUM  MONOXIDE,  BaO,  often  called  baryta,  is  prepared, 
like  strontium  monoxide,  by  calcining  the  nitrate.    It  forms  a  gray, 
porous  mass,  which  absorbs  moisture  and  carbon  dioxide  from  the 


BARIUM.  271 

air.  If  a  fragment  of  this  substance  be  sprinkled  with  a  few 
drops  of  water,  barium  hydrate  is  formed  with  such  energy  that 
the  mass  sometimes  becomes  red  hot. 

449.  BARIUM  HYDRATE,  BaOH,  is  made  by  dissolving  the 
oxi  le  in  boiling  water,  which  dissolves  about  one-tenth  its  weight. 
When  the  liquid  cools,  the  greater  part  of  the  hydrate  is  deposited 
in  Colorless  crystals  which  contain  Ba(OH /  -f-  8H20.  These  crys- 
tals are  soluble  in  water,  and,  under  the  name  baryta  water,  their 
solution  is  used  for  the  precipitation  of  carbon  dioxide  as  insoluble 
bai  ium  carbonate,  or  for  the  precipitation  of  sulphuric  acid. 

50.  BARIUM  DIOXIDE,  BaO2. — At  a  dull  red  heat,  barium 
monoxide  will  absorb  oxygen,  and  become  converted  into  the  di- 
oxi  ie,  which  is  made  by  passing  oxygen  over  the  monoxide  heated 
in  .  porcelain  tube  or  in  a  crucible.  Barium  dioxide  is  a  grayish- 
wli  te  substance,  which,  when  thrown  into  water,  crumbles  to  a 
wli  te  hydrate.  It  loses  one  atom  of  oxygen  at  a  bright  red  heat, 
au<  the  monoxide  remains.  By  the  action  of  strong  sulphuric 
aci  1,  barium  dioxide  is  converted  into  barium  sulphate,  while  ozone 
is  <  isengaged.  With  hydrochloric  acid,  the  hydrated  dioxide  yields 
barium  chloride  and  hydrogen  dioxide. 

-;51.  TESTS  FOR  BARIUM. — Hydrogen  sulphide  occasions  no 
precipitate  in  solutions  of  barium  salts.  Sodium  carbonate  throws 
dovn  white  barium  carbonate.  Sulphuric  acid  precipitates  insol- 
uble barium  sulphate,  even  in  exceedingly  dilute  solutions,  and 
the  precipitate  is  insoluble  in  nitric  acid,  either  cold  or  boiling. 
Barium  salts  communicate  a  green  color  to  flame. 

The  barium  salts  are  very  poisonous. 

452.  The  nitrates  of  barium  and  strontium  are  employed  in  pyrotechny,  for 
they  impart  to  fireworks  the  characteristic  flame  colors  of  the  metals. 

A  red  fire  may  be  made  by  mixing  30  parts  of  potassium  chlorate,  17  parts 
of  sulphur,  2  of  charcoal,  and  45  of  strontium  nitrate.  The  materials  must 
be  |  ulverized  separately,  and  may  be  mixed  by  repeated  passing  through  a 
?iev<!.  A  green  fire  may  be  made  by  similarly  mixing  33  parts  of  potassium 
chlo-ate,  10  of  sulphur,  5  of  charcoal,  and  52  of  barium  nitrate.  If  it  be 
desired  that  the  fires  shall  produce  little  or  no  smoke,  the  following  formulae 
may  be  used;  the  ammonium  picrate  may  be  made  by  adding  ammonia- 
water  to  a  concentrated  alcoholic  solution  of  picric  acid,  until  the  liquid  has 
an  ammoniacal  odor,  and  then  collecting  and  carefully  drying  the  precipitate. 


272  LESSONS    IN    CHEMISTRY. 

Ammonium  Ferrous  Strontium  Barium 

picrate.  picrate.  nitrate.  nitrate. 

Yellow 50  50 

Green 48  ...  ...  52 

Red 54  ...  46 

The  stars  for  rockets  and  Roman  candles  are  made  by  moistening  the  colored 
fires  and  forming  them  into  small  balls;  these  are  dried  and  introduced  into 
the  tube,  from  which  they  are  projected  by  a  small  charge  of  gunpowder. 


LESSON    LII. 
LEAD.    Pb  =  207. 

453.  In  many  of  its  chemical  relations,  lead  resembles  calcium,  strontium, 
and  barium,  and  it  might  be  classed  in  the  same  group  of  metals ;  but  in  a 
number  of  its  compounds  it  acts  as  a  tetratomic  element.  It  forms  a  dioxide, 
PbO2,  and  a  tetrachloride,  PbCl4.  In  the  dioxides  of  strontium  and  barium, 
it  is  not  probable  that  the  atoms  of  these  metals  are  tetratomic :  it  appears 
rather  that  the  two  atoms  of  oxygen  are  related  to  each  other,  while  each  is 
also  related  to  the  atom  of  metal.  In  lead  dioxide  the  lead  atom  is  tetratomic. 

454.  The  principal  lead  ores  are  galena,  which  is  lead  sulphide, 
and  cerusite,  which  is  the  carbonate.  The  reduction  of  the  latter 
mineral  is  an  exceedingly  simple  process :  it  is  heated  with  char- 
coal ;  the  reduced  lead  collects  on  the  hearth  of  the  furnace,  and 
is  drawn  off  as  it  accumulates. 

Galena  may  be  reduced  by  heating  it  with  scrap  iron:  iron 
sulphide  and  lead  are  formed,  and,  the  lead  being  the  heavier,  the 
iron  sulphide  floats  on  the  surface  and  is  drawn  off  as  slag.  The 
more  usual  process,  known  as  the  reaction  process,  consists  in 
heating  the  galena  on  the  hearth  of  a  reverberatory  furnace  (Fig. 
112)  provided  with  openings  (D)  for  the  admission  of  air.  Part 
of  the  lead  sulphide  is  so  converted  into  oxide,  and  another  portion 
into  sulphate.  When  this  reaction  has  sufficiently  advanced,  the 
openings  of  the  furnace  are  closed,  and  the  heat  is  increased. 
Under  these  circumstances  the  unaltered  sulphide  reacts  with  both 
oxide  and  sulphate,  metallic  lead  being  formed,  while  sulphur 
dioxide  is  disengaged. 

PbS    +    2PbO     =    3Pb    +    SO2 
PbS     +     PbSO*    =     2Pb     +     2S02 


LEAD. 


273 


Sometimes  charcoal  powder  is  added  after  the  air-openings  are 
closed,  in  order  to  aid  in  the  reduction  of  the  oxide  and  sulphate. 


Lead  is  a  bluish -white  metal,  having  a'  brilliant  lustre,  which 
so<  n  tarnishes  by  exposure  to  air.  It  is  soft,  and  can  be  scratched 
by  the  finger-nail :  it  is  quite  malleable,  but  has  so  little  tenacity 
th;  t  it  cannot  readily  be  drawn  into  wire.  Its  density  is  about 
11  36  :  it  melts  at  about  330°.  It  may  be  crystallized  by  allow- 
ing a  crucible  full  of  the  molten  metal  to  cool  until  a  crust  forms 
on  its  surface,  piercing  the  crust,  and  pouring  out  the  still  liquid 
interior.  The  interior  of  the  crucible  is  then  found  to  be  lined 
with  octahedral  crystals.  Molten  lead  absorbs  oxygen  from  the 
air.  and  its  surface  becomes  covered  with  a  film  of  lead  oxide,  PbO. 

Lead  is  dissolved  by  boiling  hydrochloric  acid,  lead  chloride 
being  formed  while  hydrogen  is  disengaged.  It  is  scarcely  af- 
fected by  dilute  sulphuric  acid,  but  the  strong  acid  dissolves  it 
by  the  aid  of  heat,  sulphur  dioxide  being  given  off.  Nitric  acid 
converts  it  into  lead  nitrate,  and  disengages  red  vapors. 

Pure  water  containing  dissolved  air  and  carbon  dioxide  dissolves 
a  small  quantity  of  lead  in  the  form  of  hydrate  and  carbonate,  and 
for  this  reason  lead  is  an  unsafe  metal  for  lining  rain-water  cisterns 
intended  for  storing  drinking-water.  Most  spring-  and  river-waters 
contain  small  quantities  of  sulphates :  when  such  water  flows 
s 


274  LESSONS   IN   CHEMISTRY. 

through  lead  pipes,  the  surface  of  the  metal  becomes  quickly  cov- 
ered with  a  film  of  insoluble  lead  sulphate,  which  protects  the 
pipe  from  further  action,  and  the  water  from  being  poisoned  by 
the  introduction  of  lead  compounds. 

Lead,  and  all  its  soluble  compounds,  as  well  as  such  as  may  be  rendered 
soluble  by  the  juices  of  the  stomach,  are  poisonous,  and  the  poisonous  effects 
are  cumulative.  Workmen  employed  in  the  manufacture  of  white  lead,  red 
lead,  and  other  lead  compounds,  frequently  suffer  from  chronic  lead-poisoning, 
as  do  also  painters  and  color-grinders.  Small  quantities  of  lead  are  then  accu- 
mulated in  the  system,  and  cause  peculiar  disorders,  among  which  lead  colic 
is  the  most  common :  one  of  the  characteristic  symptoms  of  lead-poisoning  is 
a  peculiar  blue  line  around  the  borders  of  the  gums.  The  workmen  in  lead- 
works  usually  drink  small  quantities  of  an  exceedingly  dilute  sulphuric  acid, 
by  which  the  lead  in  the  system  is  converted  into  the  insoluble  and  innocuous 
sulphate.  In  cases  of  chronic  lead-poisoning,  the  administration  of  potassium 
iodide  removes  the  metal  from  the  tissues  by  the  formation  of  lead  iodide, 
which  is  soluble  in  solutions  of  potassium  iodide,  and  can  consequently  be 
eliminated  by  the  excretory  organs. 

Metallic  lead  is  used  in  the  form  of  sheets  for  roofing  and  lining 
tanks ;  it  is  manufactured  into  lead  pipe ;  type  metal,  which  is  80 
per  cent,  lead  and  20  per  oent.  antimony ;  pewter,  which  contains 
between  eighty  and  ninety  per  cent,  tin,  the  remainder  being  lead ; 
and  plumbers'  solder,  an  alloy  of  lead  and  tin.  Enormous  quantities 
of  lead  are  employed  for  the  manufacture  of  shot,  which  is  made 
by  allowing  the  molten  metal  to  run  through  a  sieve,  and  the  drops 
to  fall  from  a  height  into  water.  In  common  qualities  of  tin  plate, 
a  large  proportion  of  the  coating  is  lead  instead  of  pure  tin. 

455.  LEAD    CHLORIDE,  PbCP,  is   prepared   by  boiling  lead 
oxide  in  hydrochloric  acid,  and  is  precipitated  when  hydrochloric 
acid  or  a  soluble  chloride  is  added  to  the  solution  of  a  lead  salt. 
It  is  a  white  solid,  only  slightly  soluble  in  cold  water,  but  dis- 
solving in  thirty-three  times  its  weight  of  boiling  water :  when 
the  hot  solution  cools,  the  chloride  separates  in  brilliant  anhydrous 
needles.     It  is  employed  in  the  manufacture  of  several  yellow 
colors,  which  are  oxychlorides  of  lead,  or  mixtures  of  the  chloride 
and  oxide. 

456.  LEAD  IODIDE,  Pbl2,  is  deposited  as  a  yellow  precipitate 
when  potassium  iodide  is  added  to  the  solution  of  a  lead  salt.     It 


LEAD   OXIDES.  275 

is  almost  insoluble  in  cold  water,  but  dissolves  in  a  little  less  than 
two  hundred  times  its  weight  of  boiling  water,  from  which  it 
separates  on  cooling  in  beautiful  golden-yellow  scales. 

-157.  LEAD  MONOXIDE,  PbO. — This  body  is  produced  by  the 
dirt  ct  oxidation  of  melted  lead  by  the  air.  It  is  an  accessory  prod- 
uct in  the  cupellation  of  lead  for  the  extraction  of  silver  (§  426). 
It  s  known  in  commerce  by  the  names  massicot  and  litharge  : 
massicot  is  a  yellow,  amorphous  powder ;  by  fusing  this  powder 
and  pulverizing  the  resulting  mass,  litharge  is  obtained  as  reddish- 
yellow,  crystalline  scales.  Lead  monoxide  is  slightly  soluble  in 
wat  ;r,  and  will  restore  the  blue  color  to  reddened  litmus.  It  melts 
at  is  red  heat,  but  cannot  be  melted  in  vessels  of  glass,  porcelain, 
or  I  lay,  because  it  combines  with  silica  and  forms  a  very  fusible 
sili<  ate,  so  destroying  the  vessel.  It  is  readily  reduced  by  char- 
coa  and  by  hydrogen.  It  is  used  in  the  manufacture  of  the  salts 
of  ead :  when  it  is  boiled  with  linseed  oil,  the  latter  acquires  the 
property  of  quickly  drying  or  hardening  when  exposed  to  the  air. 

When  the  solution  of  a  lead  salt  is  treated  with  an  alkaline 
hycrate,  lead  hydrate,  Pb(OH)2,  is  thrown  down  as  a  white  pre- 
cipitate, soluble  in  an  excess  of  the  alkaline  hydrate. 

458.  LEAD  DIOXIDE,  PbO2,  is  obtained  by  treating  red  lead 
with  nitric  acid.     Red  lead  is  a  combination  of  the  monoxide  and 
dioxide,  and  the  nitric  acid  dissolves  out  the  monoxide,  forming 
lead  nitrate,  which  is  soluble  and  can  be  washed  out,  while  the 
dioxide  remains  as  a  brown  powder.      It  is  not  soluble  in  water, 
and  by  the  action  of  heat  is  decomposed  into  lead  monoxide  and 
oxygen.     It  is  a  very  energetic  oxidizing  agent :  a  little  sulphur 
may  be  ignited  by  rubbing  it  in  a  mortar  with  some  lead  dioxide. 
It  absorbs  sulphur  dioxide,  forming  lead  sulphate  ;  with  hydro- 
chloric acid  it  forms  lead  chloride  and  water,  while  chlorine  is  dis- 
engaged. 

PbO2     +     4HC1     =     PbCl2     +     2H20     +     Cl2 

459.  RED    LEAD,    (PbO)2Pb02.— This  body   is  prepared  by 
heating  massicot  to  300°  in  furnaces  so  arranged  that  it  is  freely 
exposed  to  a  current  of  air ;  oxygen  is  then  absorbed,  and  a  beau- 
tiful red  powder,  called  minium,  or  red  lead,  is  formed.     It  is 


276  LESSONS   IN    CHEMISTRY. 

plumboso-plumbic  oxide,  but  the  proportions  of  the  monoxide 
and  dioxide  which  it  contains  are  not  constant,  though  usually 
responding  to  the  formula  given.  When  heated,  its  color  darkens  ; 
at  a  red  heat  it  loses  part  of  its  oxygen  and  is  converted  into 
the  monoxide.  Red  lead  is  employed  as  a  pigment,  and  iu  the 
manufacture  of  flint-glass,  of  which  the  brilliancy  and  refractive 
power  are  due  to  silicate  of  lead.  Mixed  into  a  paste  with  linseed 
oil,  it  forms  an  excellent  cement. 

460.  LEAD   SULPHIDE,  PbS. — This  compound  is  the  mineral 
galena,  which  is  found  in  cubical  crystals  of  a  bluish-gray  color 
and  metallic  appearance.     Its  density  is  7.58 ;  it  is  much  harder 
than  lead,  and  rather  brittle.     It  melts  when  heated  to  redness, 
and  in  contact  with  air  is  then  oxidized  to  sulphide  and  sulphate. 
It  is  converted  into  lead  chloride  by  boiling  with  hydrochloric 
acid,  hydrogen  sulphide  being  disengaged.     Boiling  nitric  acid 
converts  it  into  lead  sulphate. 

461.  TESTS  FOR  LEAD. — With  the  exception  of  the  nitrate 
and  acetate,  none  of  the  more  common  lead  salts  are  very  soluble. 
Those  which  are  soluble  have  a  sweet  and  somewhat  astringent 
taste.     Hydrogen  sulphide  forms  in  them  a  black  precipitate  of 
lead  sulphide :  potassium  and  sodium  hydrates  and  ammonia  pro- 
duce white  precipitates,  which  are  soluble  in  an  excess  of  either 
of  the  first  two  reagents.     Sulphuric  acid  yields  a  white  precipi- 
tate even  in  the  most  dilute  solutions  :    hydrochloric  acid  throws 
down  white  lead  chloride,  unless  the  solution  be  too  dilute  ;  this 
precipitate  is  dissolved  by  boiling,  an,d,  on  cooling  again,  sepa- 
rates in  crystals.      Potassium  chromate  precipitates  yellow  lead 
chromate,  which  is  soluble  in  the  alkaline  hydrates. 

If  a  salt  of  lead  be  mixed  with  sodium  carbonate,  and  heated 
on  a  piece  of  charcoal  in  the  inner  flame  of  a  blow-pipe,  a  small 
bead  of  metallic  lead  is  obtained,  and  the  softness  of  the  bead 
indicates  the  nature  of  the  metal. 


MAGNESIUM.  277 

LESSON    LIIL 
MAGNESIUM.— ZINC.— CADMIUM. 

62.  These  three  metals  form  a  natural  group,  to  which  belongs  also  a 
foi  rth,  glucinuin,  of  which  the  silicate  constitutes  part  of  the  mineral  beryl 
an  I  the  green  precious-stone  emerald.  They  are  diatomic  metals. 

463.  Magnesium,  Mg  —  24. — This  element  occurs  in  nature 
a.<  carbonate  in  the  mineral  magmsite,  as  sulphate  in  kieserite,  and 
as  silicate  in  serpentine  and  soapstone.     The  metal  is  obtained  by 
In  ating  its  chloride  with  sodium  in  an  iron  crucible,  a  mixture  of 
common  salt  and  calcium  fluoride  being  added  as  a  flux.     The  so- 
di  im  is  converted  into  sodium  chloride,  and  the  magnesium  sepa- 
ra  es  in  little  globules  diffused  through  the  molten  mixture,  which 
is  constantly  stirred.     When  perfectly  cold,  the  mass  is  broken  up, 
ai.d  the  globules  of  magnesium  are  removed  and  heated  to  red- 
m  3s  in  a  small  charcoal  vessel  in  a  current  of  hydrogen.     Pure 
m  ignesium  volatilizes,  and  condenses  in  the  cooler   part  of  the 
aj  paratus. 

Magnesium  is  a  bluish-white  metal ;  its  surface,  which  is  not 
very  brilliant,  soon  tarnishes  in  the  air.  Its  density  is  about 
1.75.  It  is  both  ductile  and  malleable,  and  is  ordinarily  rolled 
into  ribbon  or  drawn  into  wire.  It  slowly  decomposes  water  at 
ordinary  temperatures,  and  more  rapidly  at  the  temperature  of 
boiling.  It  melts  at  500°,  and  if  exposed  to  the  air  takes  fire 
and  burns  with  great  brilliancy.  The  light  of  burning  mag- 
nesium is  very  bright,  and  lamps  are  constructed  in  which  the 
ribbon  is  gradually  supplied  by  clock-work.  Such  lamps  are  em- 
ployed in  photographing  the  interior  of  caves  and  other  dark 
localities.  The  product  of  the  combustion  is  magnesium  oxide, 
MgO, 

464.  MAGNESIUM  CHLORIDE,  MgCP. — When  magnesium  or 
its  oxide  or  carbonate  is  dissolved  in  hydrochloric  acid,  and  the 
solution  is  concentrated,  crystals  of  magnesium  chloride,  with  six 
molecules  of  water  of  crystallization,  are  obtained.     These  crystals 

24 


278  LESSONS    IN    CHEMISTRY. 

cannot  be  rendered  anhydrous,  and  their  solution  cannot  be  evap- 
orated to  dryness,  for  they  decompose  into  hydrochloric  acid  and 
magnesium  oxide. 

MgCl»         +         H2Q         -         MgO         +         2HC1 

Anhydrous  magnesium  chloride  is  prepared  by  dissolving  the 
oxide  or  carbonate  in  hydrochloric  acid,  and  adding  two  molecules 
of  ammonium  chloride  for  every  atom  of  magnesium.  This  so- 
lution may  be  evaporated  to  dryness,  and  leaves  an  anhydrous 
double  chloride  of  magnesium  and  ammonium.  The  double  salt 
is  heated  in  a  clay  crucible  until  all  of  the  ammonium  chloride  is 
driven  off,  while  the  magnesium  chloride  remains  in  a  state  of 
fusion  ;  on  cooling,  it  solidifies  to  a  pearly-white  mass.  In  this 
form  it  is  used  for  the  manufacture  of  magnesium.  It  is  very 
soluble  in  water,  but  from  the  solution  only  the  hydrated  crystals 
can  be  obtained. 

465.  MAGNESIUM  OXIDE,  MgO. — This  is  the  calcined  mag- 
nesia of  the  pharmacies.     It  is  made  by  calcining  magnesium  car- 
bonate, or  the  mixture  of  hydrate  and  carbonate  commonly  called 
white  magnesia.     It  is  a  tasteless  white  powder,  infusible  even  at 
very  elevated  temperatures.     It  is  insoluble  in  water,  but  com- 
bines with  that  liquid,  forming  magnesium  hydrate,  Mg(OH)2,  a 
substance  which  restores  the  blue  color  to  reddened  litmus.     This 
same  hydrate  is  precipitated  when  an  alkaline  hydrate  is  added  to 
the  solution  of  a  magnesium  salt. 

466.  TESTS  FOR  MAGNESIUM. — Neither  hydrogen  sulphide  nor 
ammonium  sulphide  occasions  any  precipitate  in  magnesium  solu- 
tions.    Sodium  carbonate  throws  down  a  white,  flocculent  precipi- 
tate of  the  hydrated  carbonate,  which  when  dried  in  the  air  con- 
stitutes white  magnesia.     Potassium  and  sodium  hydrates  yield 
white  precipitates  of  the  hydrate,  as  does  also  ammonia  unless  the 
solution  be  acid  or  contain  ammonium  chloride.     Sodium  phos- 
phate with  a  few  drops  of  ammonia  produces  a  white,  crystalline 
precipitate  of  ammonio-magnesium  phosphate,  Mg(NH4)P04. 

467.  Zinc,  Zn  =  65.2. — The  ores  from  which  zinc  is  obtained 
are  the  carbonate,  which  is  called  calamine,  and  the  sulphide, 
called  blende.     These  minerals  are  broken  up  and  roasted  in  fur- 


ZINC. 


279 


naoes  much  resembling  lime-kilns.  Ar  the  temperature  of  the 
rousting,  which  is  a  dull  red  heat,  the  calamine  loses  carbon  dioxide 
an  1  the  water  which  it  usually  contains,  and  is  converted  into  zinc 
ox  de:  the  sulphide  is  also  oxidized  by  roasting,  sulphur  dioxide 
be;ng  disengaged.  The  zinc  oxide  so  obtained  is  mixed  with  char- 
co:.l  and  heated  for  about  twenty-four  hours  to  a  high  temperature 
in  clay  or  iron  vessels :  carbon  monoxide  is  disengaged,  while  the 
zii  o  volatilizes  and  is  condensed  in  suitable  apparatus.  Various 
pr-  >eesses  of  distillation  are  employed :  we  need  only  consider  the 
twj  which  are  generally  used.  In  the  Belgian  process,  the  mix- 
tu  e  of  zinc  oxide  and  charcoal  is  introduced  into  clay  tubes,  closed 
at  one  end,  and  inserted  in  an  inclined  position  in  the  walls  of  the 
fu  nace;  to  the  open  and  exterior  end  of  each  tube  is  adapted  a 
bu  ged  pipe,  in  which  the  zinc  vapor  condenses  and  the  metal  col- 
lc(  :s.  In  order  that  no  air  may  enter  the  tubes  and  oxidize  the 
zii  c,  a  sheet-iron  noz- 
zk  having  a  hole  for 
til*  exit  of  the  gases, 
is  passed  over  the  ex- 
tre  nity  of  this  con- 
denser (Fig.  114). 
Th  3  tubes  are  usu- 
ally about  a  metre  in 
length,  and  twenty 
centimetres  in  inte- 
rior diameter.  A  large  number  of  them  are  placed  in  parallel 
rows  in  the  same  furnace :  when  all  the  zinc  has  distilled,  the 
receivers  containing  it  are  removed,  and  a  fresh  charge  of  roasted 
ore  and  charcoal  is  introduced  into  the  tubes. 

In  the  Silesian  process,  the  retorts  are  arched,  and  very  similar 
in  form  to  those  employed  in  the  manufacture  of  illuminating  gas 
from  coal. 

4(58.  At  present,  the  furnace  used  in  the  reduction  of  zinc  by  both  the  Bel- 
gian and  Silesian  methods  is  that  known  as  the  Siemens  regenerative  furnace, 
which  effects  a  great  saving  of  fuel.  In  this  arrangement,  the  cool  is  fed  grad- 
ually to  the  grate  of  a  peculiar  fire-box,  called  the  generator,  and  the  admis- 
sion of  air  is  there  so  regulated  that  as  much  carbon  monoxide  as  possible  may 


FlG.   114. 


280 


LESSONS   IN    CHEMISTRY. 


be  produced  by  an  imperfect  combustion ;  in  addition,  the  ashes  below  the 
grate  are  kept  moist,  and  the  steam  passing  into  the  fire  reacts  with  the  hot 
carbon,  producing  hydrogen  and  carbon  monoxide  (g  232) ;  the  highly-heated 
gas  is  led  through  a  chamber  filled  with  fire-bricks,  which  become  very  hot; 
by  a  system  of  dampers,  the  gases  are  then  directed  through  another  similar 
chamber,  while  air  is  admitted  to  that  which  has  been  heated ;  the  heated  air 
from  the  one,  and  the  heated  gas  from  the  other,  are  then  brought  in  contact 
where  it  is  desired  that  the  greatest  temperature  shall  be  produced  by  the  per- 
fect combustion  of  the  gases.  The  heat  of  the  waste  products  of  combustion 
is  applied  to  heating  other  fire-brick  chambers,  which  will  afterwards  serve  for 

the  admission  of 
nir,  a?  these  regen- 
erators, as  they  are 
called,  are  cooled 
by  the  entering 
air.  Figure  115 
represents  the  fire- 
brick chambers  of 
a  Siemens  furnace 
applied  to  the  Si- 
lesian  zinc  process. 
The  two  chambers 
on  each  side  serve 
alternately,  one 
for  the  entrance 
of  air,  and  one  for 
the  gas  from  the 
generator,  while 
the  other  two  serve 
for  the  exit  of  the 
products  of  com- 
bustion. The 
heated  air  and  gas 
from  A  and  A' 
come  in  contact  in 

the  space  B,  and  the  flames  play  through  openings  in  the  floor  above  which 
are  the  clay  retorts.  The  heated  products  of  combustion  pass  over  the  retorts 
in  another  similar  chamber,  C,  and  from  above  downwards  through  other  fire- 
brick chambers,  D  and  D'.  The  dampers  allow  the  direction  of  the  current  of 
gas  and  air  to  be  reversed  from  A  A'  to  D  D'  as  often  as  necessary,  and  in 
practice  it  is  so  changed  about  once  every  hour. 

Zinc  must  usually  be  purified  before  it  is  sent  into  commerce, 
and  the  most  harmful  impurity  is  lead,  for  it  impairs  the  mallea- 
bility of  the  zinc.  The  lead  is  separated  in  great  part  by  melting 


FIG.  115. 


ZINC.  281 

tin  zinc  in  moulds  which  are  slightly  inclined  and  have  a  cavity  at 
th-j  lower  end:  in  this  the  greater  part  of  the  lead  collects  by 
re.ison  of  its  greater  density,  and  may  be  broken  from  the  cooled 
iirjjot.  Commercial  zinc  usually  contains  small  quantities  of  iron, 
cupper,  lead,  cadmium,  and  sometimes  arsenic.  Sheet  zinc  is  the 
purest. 

Zinc  is  a  bluish-white  metal,  capable  of  taking  a  high  lustre. 
Its  density  varies  from  6.86,  that  of  the  cast  metal,  to  7,  that  of 
tha  rolled.  Pure  zinc  may  be  hammered  into  sheets,  or  drawn 
in  o  wire  at  ordinary  temperatures,  but  commercial  zinc  must  be 
re  Jed  at  about  150°.  It  again  becomes  brittle  at  200°,  and  may 
n  idily  be  pulverized  in  a  mortar  heated  to  that  temperature.  It 
m  ?lts  at  410°,  and  distils  at  about  1000°.  It  is  unaltered  by  dry 
ai ',  but  in  moist  air  its  surface  becomes  dull  from  the  formation 
o!  a  film  of  hydrated  carbonate,  which  protects  the  metal  from 
fi  rther  action. 

When  it  is  heated  to  redness  in  the  air,  it  takes  fire  and  burns 
w  th  a  bluish  flame,  giving  off  clouds  of  white  zinc  'oxide,  ZnO. 
F  ne  zinc  shavings  may  be  lighted  by  a  match,  and  burn  brilliantly 
in  the  air.  If  some  zinc  be  heated  to  redness  in  a  ladle  or  cruci- 
bl<]!,  and  pieces  of  potassium  nitrate  be  thrown  in,  the  oxygen  of 
the  decomposing  nitre  energetically  oxidizes  the  metal. 

Zinc  is  dissolved  by  hydrochloric,  sulphuric,  and  nitric  acids, 
arid  by  boiling  solutions  of  potassium  and  sodium  hydrates.  In 
the  latter  case,  hydrogen  is  disengaged  and  an  alkaline  zincate  is 
formed,  a  compound  in  which  zinc  oxide  appears  to  act  as  an  acid 
radical.  We  have  already  studied  the  action  of  the  acids  on  zinc. 

Zinc  is  employed  in  the  manufacture  of  galvanized  iron,  which 
is  made  by  dipping  carefully  cleaned  iron  objects  into  melted  zinc; 
brass,  which  is  an  alloy  of  copper  and  zinc ;  the  plates  of  voltaic 
batteries ;  and  for  the  preparation  of  zinc  white,  which  is  zinc 
oxide. 

469.  ZINC  CHLORIDE,  ZnCl2,  may  be  formed  by  the  direct 
union  of  zinc  and  chlorine,  a  union  which  takes  place  brilliantly 
when  fine  zinc  shavings  are  thrown  into  a  jar  of  chlorine.  It  is 
prepared  by  dissolving  zinc  in  hydrochloric  acid.  It  forms  deli- 

24* 


282  LESSONS    IN    CHEMISTRY. 

quescent  crystals  containing  one  molecule  of  water  of  crystalliza- 
tion, which  is  expelled  by  heat,  and  the  anhydrous  salt  fuses  at 
250°.  The  latter  is  very  deliquescent,  and  is  an  energetic  dehy- 
drating agent.  It  is  employed  as  a  caustic  in  surgery.  Zinc 
chloride  is  very  soluble  in  water,  and  its  solution,  to  which  a  little 
free  hydrochloric  acid  and  some  ammonium  chloride  have  been 
added,  is  an  excellent  soldering  liquid,  for  moistening  the  surface 
of  iron,  zinc,  copper,  and  brass  articles  before  soldering. 

470.  ZINC  OXIDE,  ZnO,  is  prepared  on  a  large  scale  by  heating 
zinc  in  large  muffles  in  which  its  vapor  may  come  freely  in  con- 
tact with  air.     The  product  is  stirred  up  with  water ;  the  heavier 
particles  of  unaltered  zinc  sink  to  the  bottom,  while  the  zinc  oxide 
remains  suspended  in  the  creamy  liquid  which  is  rapidly  poured 
off  and  allowed  to  settle.     The  separation  of  fine  powders  by  this 
method  is  called  elutriation. 

Zinc  oxide  is  a  white  powder,  insoluble  in  water.  It  is  em- 
ployed as  a  substitute  for  white  lead  in  painting  localities  exposed 
to  hydrogen'sulphide,  which  would  blacken  a  lead  pigment. 

When  an  alkaline  hydrate  is  added  to  the  solution  of  a  zinc 
salt,  zinc  hydrate,  Zn(OH)2,  is  thrown  down  as  a  white  precipitate. 

ZnSCH     +     2KOH     =     K2SO*     +     Zn(OH)2 
This  precipitate  is  soluble  in  an  excess  of  the  alkaline  hydrate. 

471.  ZINC  SULPHIDE,  ZnS. — This  compound  is  found  native 
as  zinc  blende,  a  mineral  usually  having  a  more  or  less  intense 
brown  color,  due  to  the  presence  of  a  certain  proportion  of  iron. 
When  ammonium  sulphide  is  added  to  the  perfectly  neutral  solu- 
tion of  a  zinc  salt,  a  white  precipitate  of  hydrated  zinc  sulphide  is 
formed. 

472.  TESTS  FOR  ZINC. — Neutral  solutions  of  zinc   salts   are 
precipitated  white  by  hydrogen  sulphide ;   the  precipitate  is  not 
formed  if  free  mineral  acid  be  present.      Ammonium  sulphide 
produces  a  characteristic  white  precipitate  of  zinc  sulphide.     The 
alkaline  hydrates  and  ammonia-water  yield  white  zinc  hydrate, 
soluble  in  an   excess   of  the  reagent.      Potassium    ferrocyanide 
throws  down  a  white  precipitate  of  zinc  ferrocyanide.     The  salts 
of  zinc  are  poisonous. 


CADMIUM.  283 

473.  Cadmium,  Cd=  112. — This  metal  occurs  associated  with  zinc  in  both 
blen  le  and  calamine.  It  is  reduced  with  the  zinc,  and,  being  more  volatile 
thai  the  latter,  distils  during  the  early  part  of  the  operation.  During  the 
first  few  hours  of  the  reduction  of  many  zinc  ores,  a  brown  powder,  called 
cadtnies,  collects  in  the  receivers  attached  to  the  retorts.  This  dust  contains  a 
largo  proportion  of  cadmium  oxide,  and  when  distilled  with  charcoal  powder 
yiel  Is  an  alloy  of  zinc  and  cadmium.  The  latter  metal  is  purified  by  dis- 
solv  ng  the  alloy  in  dilute  sulphuric  acid,  precipitating  cadmium  sulphide  by 
pas- ing  hydrogen  sulphide  through  the  acid  liquid,  dissolving  the  sulphide  in 
hyd  -ochloric  auid,  and  adding  ammonium  carbonate.  Cadmium  carbonate  is 
pro*  ipitated;  this  is  collected,  dried,  and  roasted,  and  the  cadmium  oxide  ob- 
taii.  id  is  distilled  with  charcoal  powder. 

C  idmium  has  a  white  color  and  a  brilliant  lustre,  which  soon  becomes  dull 
in  i  oist  air.  Its  density  is  8.60.  It  melts  at  320°  and  boils  at  860°.  Hydro- 
chi<  ric  and  sulphuric  acids  dissolve  it  rapidly,  disengaging  hydrogen. 

1  4.  CADMIUM  IODIDE,  Cdl2,  is  made  by  digesting  cadmium  filings  and 
iodi  ic  in  water.  On  evapor;ifing  the  solution,  beautiful  transparent  and  col- 
ork  s  hexngonal  prisms  of  cadmium  iodide  are  deposited.  It  is  used  in  pho- 
tog  uphy. 

1  5.  CADMIUM  OXIDE,  CdO,  is  obtained  as  a  yellowish-brown  powder  by 
roa-  (ing  either  cadmium  nitrate  or  cadmium  carbonate.  It  is  reduced  by  hy- 
dro ;en  and  carbon  at  lower  temperatures  than  those  required  for  the  corre- 
spo  ding  reductions  of  zinc  oxide. 

•46.  CADMIUM  SULPHIDE,  CdS. — This  compound  is  found  in  nature  in  bril- 
lian :  yellow,  hexagonal  prisms.  It  is  precipitated  as  an  amorphous  yellow 
povv  ler  by  the  action  of  hydrogen  sulphide  on  solutions  of  cadmium  salts.  It 
is  ciaployed  as  a  pigment  by  artists. 

4  7.  TESTS  FOR  CADMIUM. — Potassium  and  sodium  hydrates  and  ammonia- 
wat;r  give  white  precipitates  of  cadmium  hydrate  ;  only  that  formed  by  am- 
monia is  soluble  in  an  excess  of  the  reagent.  Hydrogen  sulphide  throws 
dowa  a  characteristic  yellow  precipitate  of  cadmium  sulphide,  even  in  acid 
solutions.  Potassium  ferrocyanide  gives  a  yellowish-white  precipitate  of 
cadmium  ferrocyanide. 


LESSON    LIV. 
COPPER. 

478.  Large  deposits  of  metallic  copper  exist  on  the  shores  of 
Lake  Superior,  the  metal  being  sometimes  found  in  crystals,  some- 
times in  irregular  and  grotesque  masses.  The  more  common 


284 


LESSONS    IN    CHEMISTRY. 


copper  ores  are  cuprous  sulphide,  called  chalkosine,  and  copper 
pyrites,  a  compound  of  cuprous  sulphide  and  ferrous  sulphide. 
This  metal  is  also  found  as  cuprous  oxide,  cupric  oxide,  and  cupric 
carbonate. 

Pure  copper  ores — those  containing  only  the  oxide,  carbonate, 
or  sulphide  of  copper,  and  very  little  of  other  metals — are  easily 
reduced  :  the  sulphide  is  first  converted  into  oxide  by  roasting, 
and  the  ores  are  then  heated  with  charcoal  in  a  somewhat  con- 
ical furnace.  The  reduction  of  copper  pyrites  is  more  difficult, 
especially  if,  as  is  often  the  case,  this  mineral  be  mixed  with  the 
sulphides  of  antimony,  arsenic,  zinc,  etc.  If  such  ore  contains  a 
large  proportion  of  copper,  it  may  be  worked  by  a  dry  process;  but 
if  only  a  small  percentage  of  copper  is  present,  a  method  of  solu- 
tion is  adopted.  In  the  dry  process,  the  ore  is  first  roasted  by 
being  fed  from  hoppers  on  to  the  hearth  of  a  reverberatory  fur- 
nace (Fig.  116),  where  it  is  swept  by  the  flame  of  a  fire.  Part  of 


FIG.  116. 


the  sulphur  is  so  converted  into  sulphurous  oxide,  which  may  be 
used  for  the  manufacture  of  sulphuric  acid,  while  the  iron  and 
copper  of  the  pyrites  are  partially  converted  into  oxide  and  sul- 
phate. A  quantity  of  sand  and  silicate  of  iron  from  a  subsequent 
stage  of  the  operation  is  then  added,  and  the  mass  is  transferred 
either  to  rotating  cylindrical  furnaces  or  to  reverberatory  furnaces 
with  deep  hearths,  where  it  can  be  strongly  heated.  The  un- 


COPPER.  285 

altered  ferrous  sulphide  remaining  in  the  roasted  mass  then  reacts 
will  the  cupric  oxide  formed,  and  the  result  is  cuprous  sulphide 
and  ferrous  oxide.  The  latter  unites  with  the  sand,  forming  fer- 
rous silicate,  which  is  very  fusible,  and  is  drawn  off  as  slag,  while 
a  tolerably  pure  form  of  cuprous  sulphide  collects  on  the  hearth 
of  the  furnace.  This  product,  which  is  called  copper  matt,  is 
broken  up,  and  repeatedly  roasted  until  nearly  all  the  sulphur  is 
exp  'lied,  and  a  considerable  proportion  of  the  copper  is  reduced 
to  t  :ie  metallic  state ;  the  more  oxidmble  foreign  metals  present 
bec<  me  oxidized,  and,  on  the  addition  of  silicious  matters,  are 
con  -erted  into  fusible  silicates  by  an  increased  temperature.  The 
bla<  k  copper  so  obtained  contains  from  90  to  94  per  cent,  of 
cop  >er,  the  remainder  being  lead,  iron,  sulphur,  arsenic,  etc.  It 
is  r  fined  by  melting  it  on  the  hearth  of  a  reverberatory  furnace, 
wh(  re  the  foreign  metals  are  completely  oxidized  and  removed  as 
slaps,  while  the  copper  collects  in  a  cylindrical  cavity  made  in 
the  hearth  of  the  furnace.  It  is  solidified  by  throwing  water  on 
its  surface,  and  the  circular  masses  removed  are  called  copper 
rose  ttes.  They  are  brittle,  for  they  consist  partly  of  cupric  oxide. 
Thi-i  is  reduced  by  melting  the  rosettes  under  a  layer  of  charcoal 
powder,  arid  stirring  the  molten  metal  with  poles  of  green  wood ; 
the  combustible  gases  formed  by  the  action  of  the  high  tempera- 
ture on  the  wood  completely  deoxidize  the  copper,  and  the  cold 
metal  is  red  and  soft. 

In  the  wet  process,  used  for  poor  copper  ores,  the  latter  are  roasted  with 
from  one  to  two  or  three  per  cent,  of  common  salt  in  peculiar  rotating  fur- 
naces. Hydrochloric  acid  and  sulphurous  and  sulphuric  oxides  are  disengaged  ; 
by  passage  through  a  tall  column  filled  with  coke,  over  which  cold  water 
trickles,  these  gases  are  absorbed  for  subsequent  use  in  another  stage  of  the 
operation.  The  roasted  mass  contains  cupric  chloride  and  cupric  sulphate :  it 
is  pulverized  and  washed  with  the  water  in  which  the  gases  from  the  furnace 
have  been  condensed.  The  copper  salts  then  pass  into  solution,  while  ferric 
oxido  remains.  The  latter  is  dried  and  heated  with  charcoal  powder,  by 
which  it  is  converted  into  a  very  spongy  metallic  iron.  This  iron  is  intro- 
duced into  the  copper  solution  :  iron  salts  are  formed,  and  all  the  copper 
is  quickly  deposited  in  the  metallic  state,  together  with  any  lead,  arsenic, 
antimony,  and  silver  which  might  be  present.  The  precipitated  metal  is  col- 
lected and  melted  into  a  mass. 


286  LESSONS    IN    CHEMISTRY. 

Sometimes  copper  contains  enough  silver  to  pay  for  its  extrac- 
tion. This  may  be  accomplished  by 
melting  the  metal  with  lead  and  cast- 
ing the  alloy  into  disks :  these  are 
stood  on  edge  over  a  gutter  in  a  fur- 
nace in  which  they  may  be  heated  grad- 
ually (Fig.  117).  The  lead  melts  first, 
and  runs  out,  carrying  with  it  all  of 
FIG.  117.  the  silver.  The  mass  of  copper  is 

again  melted  and  freed  from  the  last 

traces  of  lead,  while  the  lead  which  has  removed  the  silver  is 
submitted  to  cupellation. 

Pure  copper  is  obtained  by  placing  scrap  iron  in  solution  of 
pure  cupric  sulphate,  and  thoroughly  washing  the  precipitated 
copper,  which  is  called  cement  copper.  In  certain  copper  locali- 
ties, streams  of  running  water  contain  sufficient  dissolved  copper 
sulphate,  produced  by  the  natural  oxidation  of  copper  pyrites 
on  the  lands  which  supply  the  streams,  to  pay  the  cost  of  the 
extraction  qf  the  metal.  This  is  effected  by  placing  scrap  iron  in 
troughs  through  which  the  stream  is  made  to  flow ;  the  copper 
then  deposits  on  the  iron. 

Copper  has  a  red  color  and  a  brilliant  lustre.  Its  density  is 
about  8.9.  It  is  exceedingly  ductile,  malleable,  and  tenacious. 
It  melts  at  about  1100°,  and  may  be  crystallized  either  by  fusion 
or  by  electrolysis  of  solutions  of  its  salts.  In  contact  with  the 
skin,  it  produces  a  very  unpleasant  odor. 

Copper  is  unaltered  by  cold  dry  air.  but  by  moist  air  it  is 
gradually  converted  into  a  hydrocarbonate,  which  appears  in  green 
spots  on  the  surface  of  the  metal.  This  is  the  substance  ordinarily 
called  verdigris  (see  §  333). 

At  a  temperature  about  redness,  copper  combines  directly  with 
oxygen,  forming  either  cupric  oxide,  CuO,  or  cuprous  oxide, 
Cu20,  according  to  the  access  of  air.  When  copper  acetate  is 
strongly  heated  in  a  hard  glass  tube,  it  is  entirely  decomposed, 
and  a  residue  of  finely-divided  copper  is  obtained.  If  this  be 
turned  out  and  heated  at  one  point  by  a  lighted  match,  a  black 


COPPER.  287 

spot  appears  and  rapidly  spreads  over  the  entire  mass,  which  is  so 
converted  into  cupric  oxide. 

We  have  already  studied  the  action  of  sulphuric  and  nitric 
acids  on  copper.  Hydrochloric  acid  attacks  it  only  when  boiling, 
and  then  but  slowly,  evolving  hydrogen,  and  forming  cuprous 
chlu-ide,  Cu2Cl2. 

Ai  imonia  in  presence  of  oxygen  exerts  a  curious  action  on  copper.  We  in- 
trodi  ce  some  copper  clippings  and  a  little  ammonia  into  a  bottle,  which  we 
tight  y  cork  and  then  agitate  for  a  few  minutes.  The  liquid  becomes  blue, 
and  f  we  invert  the  bottle  and  open  it  with  its  mouth  under  water,  the  latter 
will  -ise  in  the  bottle,  showing  that  part  of  the  air  has  been  absorbed.  It  is 
the  i  ^ygen  which  is  absorbed,  and  the  blue  liquid  contains  copper  nitrite  and 
amm  miacal  cupric  oxide,  both  of  which  are  soluble  in  ammonia.  This  liquid 
is  capable  of  dissolving  cotton,  linen,  paper,  and  other  forms  of  cellulose. 

C  >pper  is  used  for  the  manufacture  of  boilers,  stills,  condensing 
app.  ratus,  and  other  utensils  for  the  laboratory,  manufactory,  and 
kite  ien.  In  sheets,  it  serves  for  sheathing  ships,  and  some- 
time 3  for  roofing.  It  constitutes  part  of  many  alloys,  among 
whi(  h  are  brass,  containing  from  65  to  90  per  cent,  copper,  the 
rem;  inder  being  ziuc ;  a  large  proportion  of  copper  gives  a  red 
color  to  the  brass ;  these  metals  are  melted  together  in  crucibles, 
the  /,inc  being  added  after  the  copper  is  fused.  Bronze  contains 
from  93  to  95  per  cent,  of  copper,  the  remainder  being  tin,  with 
sometimes  1  per  cent,  of  zinc.  Gun  metal  is  about  91  per  cent, 
copper  and  9  per  cent.  tin.  Bell-metal  and  the  very  white  specu- 
lum metal  contain  respectively  78  and  67  per  cent,  of  copper,  the 
remainder  being  tin.  German  silver  is  an  alloy  of  copper,  zinc, 
and  nickel.  The  United  States  cents  contain  95  per  cent,  of 
coppor,  2.5  per  cent,  of  zinc,  and  2.5  per  cent,  of  tin. 

479.  Copper  forms  two  series  of  compounds.     It  is  a  diatomic 
element,  and  in  the  cuprous  compounds  two  atoms  of  copper  form 
a  diatomic  couple,  Cu-Cu,  which  replaces  two  atoms  of  hydrogen 
in  the  acids.     In  the  cupric  compounds,  a  single  diatomic  atom 
of  copper  replaces  two  atoms  of  hydrogen. 

480.  CUPROUS  CHLORIDE,  Cu2Cl2,  may  be  made  by  boiling  a 
solution  of  cupric  chloride  with  copper,  or  by  boiling  copper  with 
hydrochloric  acid  and  adding  a  little  nitric  acid  from  time  to  time ; 


288  LESSONS    IN    CHEMISTRY. 

in  the  latter  case,  cupric  chloride  is  formed,  and  is  at  once  re- 
duced by  the  metallic  copper  present.  On  adding  water  to  the 
brown  liquid  so  obtained,  cuprous  chloride  is  thrown  down  as  a 
white  crystalline  precipitate.  It  is  insoluble  in  water,  but  dis- 
solves in  ammonia,  forming  a  colorless  solution  which  absorbs 
oxygen  and  becomes  blue  on  exposure  to  air.  It  also  dissolves 
in  hydrochloric  acid,  and  both  of  these  solutions  are  capable  of 
absorbing  a  large  volume  of  carbon  monoxide. 

A  hydrated  compound  of  cuprous  chloride  and  cupric  oxide 
constitutes  the  beautiful  green  mineral  atacamite. 

481.  CUPRIC  CHLORIDE,  CuCP,  is  obtained  when  cupric  oxide 
is  boiled  in  hydrochloric  acid.     When  the  green  solution  is  suf- 
ficiently concentrated,  it  deposits  beautiful  bluish-green  crystals  of 
cupric  chloride,  with  two  molecules  of  water  of  crystallization. 

482.  CUPROUS  OXIDE,  Cu20. — This  substance  occurs  in  nature, 
sometimes  in  amorphous  masses,  sometimes  in  red,  regular  octa- 
hedra.     It  may  be  made  by  boiling  glucose  with  a  solution  of 
cupric  acetate,  and  is  then  thrown  down  as  a  bright-red  crystalline 
precipitate.     If  heated  in  contact  with  air,  it  is  converted  into 
cupric  oxide.     It  is  used  for  imparting  a  red  color  to  glass,  being 
added  to  the  mixture  of  sand  and  sodium  carbonate. 

483.  CUPRIC  OXIDE,  CuO. — When  cupric  nitrate  is  strongly 
heated,  it  yields  a  fine  black  powder  of  cupric  oxide.     This  com- 
pound is  usually  prepared  by  heating  metallic  copper  to  redness  in 
vessels  through  which  air  is  blown  or  drawn.     The  copper  then 
absorbs  oxygen,  and  is  converted  into  hard  and  compact  cupric 
oxide.     This  substance  is  reduced  by  both  hydrogen  and  charcoal 
at   temperatures   below  redness,  water   or  carbon  dioxide  being 
formed.     It  communicates  a  green  color  to  glass,  and  is  used  for 
that  purpose.    In  the  laboratory  it  is  of  great  value  in  the  analysis 
of  carbon  compounds. 

When  potassium  or  sodium  hydrate  is  added  to  the  solution  of 
a  cupric  salt,  cupric  hydrate,  Cu(OH)2-,  is  formed  as  a  pale-blue 
precipitate.  When  the  liquid  containing  this  hydrate  is  boiled, 
the  precipitate  turns  black,  for  it  is  converted  into  cupric  oxide 
and  water,  even  when  surrounded  by  liquid. 


COMPOUNDS    OF   COPPER.  289 

434.  CUPROUS  SULPHIDE,  Cu2S. — This  is  the  mineral  chalko- 
sine  It  may  be  obtained  as  a  black,  brittle,  crystalline  mass  by 
fusing  together  sulphur  and  copper,  or  by  burning  copper  in  vapor 
of  sulphur. 

4  ->5.  CUPRIC  SULPHIDE,  CuS,  is  thrown  down  as  a  brownish- 
blac  c  precipitate  by  the  action  of  hydrogen  sulphide  on  cupric 
solutions.  When  heated,  it  loses  sulphur,  and  is  converted  into 
cupi  ous  sulphide. 

4  S6.  CARBONATES  OF  COPPER. — When  a  solution  of  cuprous 
sulp'iate  is  treated  with  sodium  carbonate,  carbon  dioxide  is  dis- 
engiged,  and  a  bluish-green  precipitate  is  thrown  down;  when 
wasl  ed  with  warm  water,  its  color  becomes  green;  it  is  a  com- 
poui  d  of  cupric  hydrate  and  cupric  carbonate,  containing 
CuC  03.Cu(OH)2.  The  beautiful  green  mineral  malachite,  which 
whc  i  polished  displays  veins  of  variegated  tints,  is  a  compound 
havi  ig  the  same  composition.  Azurite,  a  mineral  found  in  fine 
blue  crystals,  is  a  compound  of  two  molecules  of  cupric  carbonate 
with  one  of  cupric  hydrate,  Cu(OH)2.2CuC03. 

4cL7.  TESTS  FOR  COPPER. — The  salts  of  copper  have  either  blue 
or  green  colors.  Both  hydrogen  sulphide  and  ammonium  sulphide 
throv;  down  brownish-black  precipitates.  The  alkaline  hydrates 
precipitate  pale-blue  cupric  hydrate,  insoluble  in  an  excess  of  the 
reagc  nt.  Ammonia  also  produces  a  pale-blue  precipitate,  but 
this  dissolves  when  an  excess  of  ammonia  is  added,  yielding  a 
magnificent  blue  solution  of  an  ammonio-cupric  salt. 

Potassium  ferrocyanide  produces  a  mahogany-brown  precipitate 
of  cupric  ferrocyanide,  and  the  test  is  exceedingly  delicate  and 
characteristic.  A  clean  piece  of  iron,  as  a  needle  or  knife-blade, 
dipped  in  a  cupric  solution,  quickly  becomes  covered  with  a  red 
layer  of  metallic  copper :  this  test  is  conclusive. 


25 


290 


LESSONS    IN    CHEMISTRY. 


LESSON    LV. 


MERCURY.     Hg  -  200. 

488.  Mercury  is  found  in  small  quantity  in  the  metallic  state, 
but  its  principal  ore  is  the  sulphide,  which  constitutes  the  mineral 
cinnabar.  It  is  especially  abundant  in  Spain  and  on  the  Pacific 
slope. 

The  reduction  of  cinnabar  is  a  simple  operation :  it  is  broken 
up  and  roasted  in  a  current  of  air,  the  sulphur  being  expelled  as 
sulphur  dioxide,  while  mercury  distils.  Very  little  improvement 
has  been  effected  in  the  furnaces  during  hundreds  of  years  ;  the 
mercury  vapor  is  sometimes  condensed  by  being  passed  through  a 
long  series  of  clay  pipes,  sometimes  by  being  directed  through  a 
number  of  chambers  containing  a  layer  of  water,  by  which  the 
gases  are  cooled  (Fig.  118).  The  mercury  is  then  filtered  through 


FIG.  118. 

closely-woven  canvas,  and  is  usually  transported  in  iron  bottles, 
each  bottle  holding  about  sixty  pounds. 

Mercury  is  liquid  at  ordinary  temperatures  :  it  freezes  at  — 40°, 
and  boils  at  350°.     Its  density  at  0°  is  about  13.6. 


MERCURY.  291 

The  density  of  mercury  vapor  compared  with  that  of  hydrogen  is  200:  its 
atou.ic  weight  is  also  200,  as  is  shown  by  the  vapor-densities  of  its  volatile 
compounds.  Then  if  equal  volumes  of  gases  contain  equal  numbers  of  mole- 
cule-, and  if  the  molecule  of  hydrogen  contain  two  atoms,  the  molecule  of 
men  ury  vapor  must  consist  of  a  single  atom.  We  believe  that  the  molecule 
and  itom  of  cadmium  are  identical  also,  and  for  a  similar  reason. 

Mercury  is  unaffected  by  the  air  at  ordinary  temperatures,  but 
at  .>00°  it  absorbs  oxygen  and  is  converted  into  red  mercuric 
oxi  le.  It  combines  directly,  and  in  the  cold,  with  chlorine,  bro- 
mii  u,  and  iodine,  and  with  sulphur  by  the  aid  of  a  gentle  heat,  or 
if  the  sulphur  be  finely  divided.  Mercury  is  not  dissolved  by 
hydrochloric  acid  :  boiling  sulphuric  acid  converts  it  into  mercuric 
subihate,  sulphur  dioxide  being  disengaged.  Nitric  acid  dissolves 
it,  emitting  red  vapors,  and  forming  mercurous  nitrate  if  the  re- 
act on  take  place  in  the  cold,  or  mercuric  nitrate  if  the  acid  be 
boii  .ng. 

Mercury  is  used  for  filling  thermometers,  barometers,  and  press- 
ure -gauges ;  for  silvering  ordinary  mirrors,  which  are  coated  with 
tin  foil  amalgamated  with  mercury  ;  for  the  extraction  of  silver 
and  gold  from  their  ores ;  and  for  the  preparation  of  various 
amalgams. 

1  he  mercury  of  commerce  is  rarely  pure ;  it  contains  small 
quantities  of  lead,  copper,  tin,  and  sometimes  bismuth.  Its  ap- 
proximate purity  may  be  determined  by  allowing  a  few  drops  to 
fall  on  a  clean  piece  of  paper  or  porcelain  ;  pure  mercury  will 
then  break  up  into  small  globules  which  are  perfectly  round,  and 
mov3  about  freely  when  the  surface  on  which  they  rest  is  inclined, 
but  mercury  containing  other  metals  forms  globules  that  are  drawn 
out  to  a  tail,  and  that  do  not  move  so  readily.  The  surface  of 
pure  mercury  is  perfectly  brilliant,  but  when  impure  the  metal 
has  a  tarnished  appearance.  It  may  be  purified  by  shaking  it  in 
a  bottle  with  sulphuric  acid  and  a  solution  of  potassium  dichro- 
mate  :  the  impurities  are  thus  oxidized,  and  may  be  washed  away. 

Like  copper,  mercury  is  diatomic,  and  forms  two  series  of  com- 
pounds,— mercurous  compounds,  in  which  two  atoms  form  a  di- 
atomic couple,  and  mercuric  compounds,  in  which  two  atoms  of 
hydrogen  are  replaced  by  a  single  diatomic  mercury  atom. 


292  LESSONS    IN    CHEMISTRY. 

489.  MERCUROUS  CHLORIDE,  Hg2Cl2.  —  This  compound  is  the 
well-known  medicine  calomel.    It  is  made  by  subliming  a  mixture 
of  mercurous  sulphate  and  common  salt. 

Hg2SO*  +  2NaCl         =         Na'SO*          +  HgW 

Mercurous  sulphate.  Mercurous  chloride. 

The  calomel  then  condenses  in  appropriate  receivers,  in  dense 
crystalline  masses.  It  is  usually  resublimed,  and  its  vapors  passed 
into  jars  or  chambers  filled  with  steam,  where  it  condenses  in  an 
impalpable  powder.  Calomel  is  precipitated  when  hydrochloric 
acid  is  added  to  the  solution  of  a  mercurous  salt. 

In  masses,  calomel  occurs  in  dense,  fibrous,  crystalline,  and 
translucent  fragments,  colorless  when  recently  prepared,  but  be- 
coming gray  or  yellowish  by  the  action  of  light  which  partially 
decomposes  this  compound  into  mercuric  chloride  and  mercury. 
Its  density  is  about  7.2.  It  is  insoluble  in  water  ;  when  calomel 
is  agitated  with  water  and  the  liquid  filtered,  no  turbidity  should 
be  produced  in  the  filtrate  by  the  addition  of  sodium  carbonate 
solution.  If  mercurous  chloride  be  heated  with  a  solution  of 
sodium  chloride,  it  is  converted  into  mercuric  chloride,  while 
metallic  mercury  is  deposited  as  a  gray  powder. 

490.  MERCURIC  CHLORIDE,  HgCl2,  is  the  poisonous  compound 
corrosive  sublimate.     It  is  prepared  by  subliming  a  mixture  of 
common  salt  and  mercuric  sulphate,  sodium  sulphate  being  formed 
at  the  same  time. 


HgSO*        +        2NaCl        -        Na2SO*         +         HgCl* 
Mercuric  sulphate.  Mercuric  chloride. 

It  is  also  formed  by  the  direct  combination  of  chlorine  and 
mercury. 

It  forms  dense,  white  or  colorless,  crystalline  masses,  having  a 
density  of  6.5.  It  melts  at  265°,  and  boils  at  about  295°.  It  is 
soluble  in  nineteen  times  its  weight  of  cold  water,  and  in  much 
less  boiling  water,  from  which  it  separates  in  anhydrous  crystals 
on  cooling.  It  is  exceedingly  poisonous,  and  its  antidote  is  white 
of  egg,  for  it  forms  an  insoluble  compound  with  albumen. 

491.  MERCUROUS  IODIDE,  Hg2!2,  is  obtained  as  a  green  powder 
by  rubbing  together  in  a  mortar  100  parts  of  mercury  and  63.5 


COMPOUNDS    OF    MERCURY.  293 

pans  of  iodine  with  a  few  drops  of  alcohol.  By  the  action  of 
liglt  or  heat,  it  is  decomposed  into  mercuric  iodide  and  metallic 
mercury. 

492.  MERCURIC  IODIDE,  HgP. — This  beautiful  compound  is 
prepared  by  mixing  potassium  iodide  with  four-fifths  its  weight 
of    nercuric  chloride,  both  in  aqueous  solution,  and  thoroughly 
washing  the  precipitate. 

HgCl2     +     2KI     =     HgP     +     2KC1 

If  :ither  substance  be  employed  in  excess,  the  precipitate  will  be 
red  ssolved. 

^o  obtained,  mercuric  iodide  forms  a  dark-red  powder,  which  is 
aim  >st  insoluble  in  water,  but  dissolves  slightly  in  boiling  alcohol, 
and  on  cooling  separates  in  red,  octahedral  crystals. 

Mercuric  iodide  presents  a  curious  case  of  dimorphism.  If  a 
littl )  of  the  red  powder  be  cautiously  heated  on  a  sheet  of  white 
pap  ;r  on  which  it  is  spread  out,  the  red  color  changes  to  yellow ; 
the  yellow  particles  are  rhombic  prisms,  and  if  they  be  rubbed 
witl  a  glass  rod  or  any  hard  body,  they  will  reassume  the  red  color 
and  their  first  crystalline  form,  the  octahedron.  Mercuric  iodide 
mel  s  to  a  dark-yellow  liquid,  and  volatilizes,  condensing  in  the 
yell«»w  crystals. 

^Vith  potassium  iodide,  mercuric  iodide  forms  a  soluble  com- 
pound, which  may  be  obtained  by  dissolving  the  mercuric  iodide 
in  salution  of  potassium  iodide.  The  colorless  liquid  is  called 
Nessler's  reagent,  and  is  used  in  the  laboratory  as  a  test  for  am- 
monia, and  compound  ammonias,  with  which  it  forms  a  brownish 
cloud  or  a  dense  precipitate,  according  to  the  proportion  of  am- 
monia present. 

493.  MERCUROUS  OXIDE,  Hg20. — This  substance  is  obtained 
as  a  black  powder  by  digesting  mercurous  chloride  in  a  solution 
of  potassium  hydrate.     A  temperature  of  100°,  or  the  prolonged 
action  of  light,  decomposes  it  into  mercuric  oxide  and  mercury. 

494.  MERCURIC  OXIDE,  HgO,  has  long  been  known  under  the 
name  red  precipitate.      It  may  be  made  either  by  decomposing 
mercuric  nitrate  by  heat  until  the  whole  is  converted  into  a  red 
powder  and  no  more  red  vapors  are  disengaged,  or  by  adding  po- 

26* 


294  LESSONS    IN   CHEMISTRY. 

tassium  hydrate  to  a  solution  of  mercuric  chloride  and  thoroughly 
washing  the  precipitate.  Prepared  in  the  first  manner,  it  forms 
a  red,  crystalline  powder;  obtained  by  precipitation,  it  is  yellow 
and  amorphous,  but  becomes  red  when  heated. 

Mercuric  oxide  is  insoluble  in  water :  when  it  is  heated,  its  color 
darkens,  and  at  a  temperature  of  about  400°  it  is  decomposed  into 
metallic  mercury  and  oxygen.  It  is  an  energetic  oxidizing  agent. 
In  presence  of  water,  it  converts  chlorine  into  hypochlorous  acid, 
and  when  dry  and  quite  cold,  into  hypochlorous  oxide.  If  a  mix- 
ture of  a  little  mercuric  oxide  and  sulphur  be  heated  in  a  test-tube, 
it  explodes. 

495.  MERCURIC   SULPHIDE,  HgS. — This  is  the  mineral  cin- 
nabar, which  is  found  in  hard  dense  masses,  and  in  transparent 
red  crystals.    It  is  manufactured  by  grinding  together  the  required 
proportions  of  mercury  and  sulphur,  and  subliming  the  resulting 
black  mass.     It  then  forms  a  dark-red,  crystalline  solid,  having  a 
density  of  8.12.     When  strongly  heated  out  of  contact  with  air, 
it  volatilizes  without  melting.     When  heated  in  the  air,  it  takes 
fire,  and  burns  with  a'  blue  flame,  mercury  vapor  and  sulphur 
dioxide  being  disengaged. 

The  fine  scarlet  pigment  vermilion  is  very  finely  divided  mer- 
curic sulphide,  made  by  grinding  for  a  long  time  in  a  mortar  a 
mixture  of  300  parts  of  mercury  and  114  parts  of  flowers  of 
sulphur :  75  parts  of  potassium  hydrate,  dissolved  in  400  parts 
of  water,  are  then  added,  and  the  grinding  is  continued,  the  mortar 
being  kept  at  a  temperature  of  about  45°.  When  the  powder  has 
assumed  the  desired  shade,  it  is  quickly  washed  with  hot  water, 
and  dried. 

496.  TESTS  FOR  MERCURY. — Very  few  of  the  mercurous  salts 
are  soluble :  in  their  solutions,  hydrochloric  acid  produces  a  white 
precipitate  of  mercurous  chloride ;  hydrogen  sulphide  and  potas- 
sium and  sodium  hydrates  and  ammonia  produce  black  precipitates. 

With  mercuric  salts,  hydrogen  sulphide  and  ammonium  sulphide 
give  black  precipitates ;  potassium  hydrate  throws  down  yellow 
mercuric  oxide.  If  a  piece  of  bright  copper  be  dipped  into  the 
slightly  acid  solution  of  either  a  mercurous  or  a  mercuric  salt, 


BISMUTH.  295 

metallic  mercury  is  quickly  deposited  on  the  copper,  whose  surface 
becomes  white  and  brilliant  after  a  little  friction. 

When  heated  with  lime  or  sodium  carbonate  in  a  small  glass 
tub  :,  all  compounds  of  mercury  yield  a  sublimate  of  metallic  mer- 
cury, which  condenses  in  the  cooler  part  of  the  tube  in  microscopic 
globules.  On  throwing  a  fragment  of  iodine  into  the  still  warm 
tub  i,  the  globules  are  changed  into  yellow  or  red  mercuric  iodide. 


LESSON    LVI. 
BISMUTH  AND   GOLD. 

T  icse  two  metals  are  triatomic  :  they  form  chlorides  whose  molecules  contain 
ono  itom  of  metal  and  three  atoms  of  chlorine.  They  form  trioxides,  containing 
two  atoms  of  metal  and  three  of  oxygen,  and  gold  forms  an  oxide,  Au'20. 

97.  Bismuth,  Bi  =  210. — Bismuth  is  found  in  the  metallic 
staio  disseminated  in  quartz.  It  is  separated  from  the  earthy 
ma.erials,  which  are  called  the  gangue,  by  heating  the  mineral  in 
irot  tubes  which  are  closed  at  one  end,  and  arranged  in  an  in- 
clinad  position  in  a  furnace  beyond  which  the  lower  and  open  end 
projects.  The  bismuth  then  melts  and  runs  out  of  the  tubes. 
Tin  bismuth  thus  obtained  is  never  pure,  but  contains  small 
quantities  of  other  metals,  and  sometimes  traces  of  arsenic  and 
sulj  hur.  In  order  to  purify  it,  it  is  pulverized  and  mixed  with  a 
littl  3  potassium  nitrate :  the  mixture  is  heated  to  redness  in  clay 
crucibles ;  the  impurities,  which  are  more  easily  oxidized  than 
the  bismuth,  are  thus  oxidized,  and  any  arsenic  present  is  con- 
verted into  potassium  arsenate. 

Bismuth  is  a  crystalline,  brittle,  yellowish- white  metal.  Its 
density  is  9.8.  It  melts  at  264°.  By  allowing  a  crucible  full  of 
the  molten  metal  to  cool  until  a  crust  forms  on  the  surface,  and 
then  pouring  out  the  liquid  interior  through  a  hole  made  in  the 
crust,  fine  crystals  of  bismuth  may  be  obtained.  These  crystals 
become  superficially  oxidized,  and  the  thin  film  of  oxide  imparts 
to  them  all  the  colors  of  the  rainbow.  Bismuth  is  unaffected  by 


296  LESSONS    IN    CHEMISTRY. 

cold  air,  but  at  a  red  heat  it  is  burned  to  bismuth  oxide.  It  dis- 
solves in  nitric  acid,  forming  bismuth  nitrate,  while  red  vapors  are 
disengaged. 

In  addition  to  its  use  for  the  preparation  of  the  bismuth  com- 
pounds, this  metal  is  employed  chiefly  for  the  manufacture  of 
certain  alloys.  Britannia  metal  contains  about  one  per  cent,  of 
bismuth.  The  fusing  points  of  the  bismuth  alloys  are  much 
lower  than  that  of  bismuth.  A  mixture  known  as  Wood's  alloy 
or  fusible  metal  consists  of  one  or  two  parts  of  cadmium,  two 
parts  of  tin,  four  of  lead,  and  seven  or  eight  of  bismuth.  It 
melts  between  66°  and  71°,  according  to  its  composition.  An- 
other alloy,  known  as  Arcet's  fusible  metal,  is  made  by  melting 
together  eight  parts  of  bismuth,  five  of  lead,  and  three  of  tin. 
It  melts  at  94.5°. 

Bismuth  much  resembles  antimony  in  many  of  its  chemical  re- 
lations ;  but  we  class  it  among  the  metals,  because  it  is  capable  of 
replacing  the  hydrogen  of  oxygen  acids,  so  forming  well-defined 


498.  BISMUTH   CHLORIDE,  BiCl3. — This  compound  results  from  the  direct 
union  of  chlorine  and  bismuth.     When  powdered  bismuth  is  sprinkled  into 
chlorine,  it  burns  brilliantly,  forming  the  chloride.     This  substance  is  pre- 
pared by  passing  dry  chlorine  over  melted  bismuth  in  a  retort  so  arranged 
that  the  chloride  may  collect  in  a  receiver  as  it  distils.     It  then  forms  a  crys- 
talline deliquescent  mass,  which  is  quite  soft  at  ordinary  temperatures,  being 
very  fusible.    It  is  soluble  in  hydrochloric  water,  but  is  decomposed  by  water, 
hydrochloric  acid  being  formed,  while  a  white  powder  of  bismuth  oxychloride, 
BiOCl,  is  thrown  down. 

2BiCP         +         2R2Q        =         4HC1         +         2B10C1 

Bismuth  oxychloride  constitutes  the  cosmetic  known  as  pearl-white. 

499.  BISMUTH  OXIDE,  Bi203,  is  obtained  as  a  yellow  powder  when  bismuth 
nitrate  is  strongly  heated.     It  melts  at  a  red  heat,  and  on  cooling  solidifies  to 
a  glassy,  yellow  mass.     It  forms  a  very  fusible  silicate,  and  therefore  cannot 
be  melted  in  clay  crucibles.     Bismuth  hydrate,  probably  Bi(OH)3,  is  thrown 
down  as  a  white  powder  when  bismuth  subnitrate  is  treated  with  potassium 
hydrate  or  ammonia- water. 

There  are  other  oxides  of  bismuth,  corresponding  exactly  to  the  oxides  of 
nitrogen. 

500.  BISMUTH  NITRATE,  Bi(N03)3.— When  bismuth  is  boiled 
with  nitric  acid,  and  the  solution  is  concentrated,  large,  colorless, 


GOLD.  297 

deliquescent  crystals  of  bismuth  nitrate  with  three  molecules  of 
wa'er  of  crystallization  are  deposited.  Since  bismuth  is  triatomic, 
one  atom  of  bismuth  will  replace  the  hydrogen  in  three  molecules 
of  nitric  acid,  and  combine  with  the  three  groups  NO3.  The 
crystals  of  bismuth  nitrate  are  very  soluble  in  water  containing 
fro  j  nitric  acid ;  but  if  the  solution  be  diluted  with  a  large  volume 
of  water,  a  pulverulent  white  precipitate  is  thrown  down.  This 
coi  tains  (BiO)NO3,  or  BiNO4,  and  is  employed  in  medicine  under 
the  name  sub  nitrate  of  bismuth.  A  larger  quantity  may  be  ob- 
tained by  adding  very  dilute  ammonia  to  the  liquid. 

•  »01.  TESTS  FOR  BISMUTH. — When  solutions  of  the  bismuth 
sal's  are  largely  diluted  with  water,  white  precipitates  of  sub-salts 
arc  thrown  down.  Hydrogen  sulphide  and  ammonium  sulphide 
occ  ision  brown  precipitates  of  bismuth  sulphide.  The  alkaline 
car  )onates  and  hydrates  yield  white  precipitates,  insoluble  in  an 
exi  ess  of  the  reagent. 

Vhen  a  bismuth  salt  is  heated  with  sodium  carbonate  in  the 
intnr  flame  of  a  blow-pipe,  a  brittle  bead  of  metallic  bismuth  is 
obt  lined. 

«r>02.  Gold,  Au  —  197.— Gold  is  found  in  the  metallic  state, 
sometimes  in  masses  called  nuggets,  but  more  usually  in  small 
par  icles  disseminated  through  quartz  rock,  or  the  sand  produced 
by  ihe  disintegration  of  the  rock.  It  is  sometimes  associated  with 
silver,  copper,  lead,  and  tellurium.  The  gold  is  extracted  from 
gold-bearing  sand  by  washing  the  latter  in  a  stream  of  running 
wator  in  troughs  called  cradles.  By  reason  of  its  great  density, 
the  gold  then  sinks  to  the  bottom,  while  the  lighter  sand  is  carried 
on  with  the  water.  The  gold  may  then  sometimes  be  removed  at 
once;  sometimes  it  is  in  such  small  particles  that  it  must  be  amal- 
gamated with  mercury,  as  will  presently  be  described.  Quartz 
rock  containing  gold  is  crushed  by  powerful  machinery,  and  the 
greater  part  of  the  earthy  matter  is  removed  by  washing  in  vessels 
containing  mercury,  which  forms  an  amalgam  with  the  gold.  Fig. 
119  represents  an  apparatus  which  is  sometimes  employed  for 
grinding  together  the  mercury  and  crushed  rock.  It  consists  of 
inclined  iron  basins,  each  containing  two  cast-iron  balls:  the  rock 


298  LESSONS    IN    CHEMISTRY 

and  mercury  being  introduced  into  these  vessels,  a  motion  of  rota- 
tion is  communicated  by  machinery,  and  by  the  friction  of  the 


FIG.  119. 

balls  the  rock  is  reduced  to  an  impalpable  powder,  which  is  carried 
off  by  a  current  of  water  flowing  through  the  basins,  while  the 
gold  amalgamates  with  the  mercury.  The  amalgam  is  compressed 
in  chamois-skin  or  canvas  bags,  through  which  the  excess  of  mer- 
cury is  forced,  and  the  solid  amalgam  remaining  in  the  bags  is 
then  heated  in  iron  retorts.  The  mercury  distils,  while  the  gold 
remains. 

On  the  Pacific  slope  large  quantities  of  gold  are  obtained  by 
hydraulic  mining,  which  is  conducted  by  throwing  streams  of 
water  with  great  force  against  the  soft  and  disintegrated  rocks 
containing  the  gold.  The  stream  of  water,  flowing  from  these  rocks, 
and  carrying  with  it  the  gold  and  mud,  and  even  large  stones,  is 
conducted  through  sluices  into  settling-troughs  containing  mer- 
cury, which  removes  the  gold. 

As  extracted  from  its  native  rocks  or  sand,  gold  is  rarely  pure. 
It  usually  contains  more  or  less  silver ;  this  may  be  removed  by 
boiling  the  metal  in  nitric  acid,  which  does  not  affect  the  gold, 
while  it  converts  the  silver  into  silver  nitrate.  However,  if  only 
a  small  proportion  of  silver  be  present,  that  metal  is  protected 
by  the  gold,  and  it  is  necessary  to  melt  the  alloy  with  a  larger 
proportion  of  silver  before  boiling  it  with  nitric  acid.  The  gold 
then  remains  as  a  spongy  mass.  Pure  gold  may  also  be  obtained 
by  adding  ferrous  sulphate  or  oxalic  acid  to  a  solution  of  gold 


AURIC   CHLORIDE.  299 

ch  oride ;  in  this  case  the  gold  is  thrown  down  as  a  dark-brown, 
dull  powder,  capable  of  assuming  its  natural  high  lustre  by 
burnishing. 

The  color  of  gold  varies  from  greenish  yellow  to  a  red  almost 
as  decided  as  that  of  copper.  Light  which  has  been  successively 
rellected  from  ten  surfaces  of  gold  is  scarlet.  Gold  is  very  soft, 
an  1  the  most  malleable  and  ductile  of  the  metals.  Its  density  is 
195;  it  melts  at  about  1200°,  and  at  a  higher  temperature  emits 
a  ^reen  vapor.  A.  thin  gold-leaf,  carefully  spread  out  between 
tw )  plates  of  glass,  allows  the  passage  of  a  faint  green  light. 

Gold  is  not  oxidized  by  air,  either  moist  or  dry,  or  at  any  tem- 
pt' ature.  It  is  not  affected  by  boiling  with  nitric,  sulphuric,  or 
h}  Irochloric  acids.  Nitro-hydrochloric  acid  dissolves  it,  disen- 
gaging red  vapors,  and  forming  a  yellow  solution  of  gold  tri- 
ch  oride  ;  the  nitro-hydrochloric  acid  employed  for  dissolving  gold 
is  a  mixture  of  nitric  acid  with  four  times  its  weight  of  hydro- 
ch  oric  acid.  Gold  is  also  attacked  by  selenic  acid,  H2SeO-,  by  a 
ho  mixture  of  iodic  and  sulphuric  acids,  and  by  a  boiling  mixture 
of  concentrated  nitric  and  sulphuric  acids ;  from  the  latter  solu- 
tion the  gold  is  again  deposited  in  the  metallic  state  by  the  addi- 
tion of  water.  Gold  dissolves  readily  in  chlorine-water,  in  bromine, 
anu  combines  directly  with  iodine  under  the  influence  of  light. 

Gold  forms  two  series  of  compounds, — aurous  compounds,  in 
which  the  metal  appears  to  be  monatomic,  and  auric  compounds, 
in  which  it  is  triatomic. 

503.  AURIC  CHLORIDE,  AuCl3. — When  the  solution  of  gold  in 
nitro-hydrochloric  acid  is  evaporated,  auric  chloride  is  deposited  as 
a  dark-red  crystalline  mass,  which  is  very  deliquescent.  It  is  very 
soluble  in  water  and  in  ether.  Its  strong  solutions  are  orange 
brown,  but  the  dilute  solution  is  pure  yellow.  It  produces  a  violet 
stain  on  the  skin  ;  it  is  decomposed  by  the  action  of  heat,  and 
more  slowly  by  light,  and  is  reduced  by  many  substances,  among 
which  are  phosphorus,  phosphorous  and  sulphurous  acids,  oxalic 
acid,  and  ferrous  sulphate.  A  stick  of  phosphorus  immersed  in 
an  ethereal  solution  of  auric  chloride  becomes  quickly  coated 
with  a  film  of  gold.  The  metal  is  deposited  as  a  brown  powder 


300  LESSONS    IN    CHEMISTRY. 

when  either  ferrous  sulphate  or  oxalic  acid  is  added  to  a  solution 
of  auric  chloride. 

When  a  solution  containing  a  mixture  of  stannous  and  stannic 
chlorides  is  added  to  auric  chloride,  a  flocculent,  purple  precipi- 
tate of  uncertain  composition,  but  containing  gold,  tin,  oxygen,  and 
hydrogen,  is  thrown  down.  This  precipitate  is  known  as  purple 
of  Cassius,  and  is  employed  in  painting  on  glass  and  porcelain. 

When  auric  chloride  is  heated  to  230°,  chlorine  is  disengaged, 
and  an  insoluble  yellow  powder  of  aurous  chloride,  AuCl,  remains. 

There  are  two  oxides  of  gold, — aurous  oxide,  Au'20,  and  auric 
oxide,  Au203.  The  first  is  basic,  the  second  forms  aurates  with 
the  metals.  When  caustic  alkalies  are  fused  with  gold  in  contact 
with  air,  alkaline  aurates  are  formed. 

504.  ASSAYING  OF  GOLD. — Gold  coin,  jewelry,  etc.,  are  generally  alloyed 
with  silver,  and  sometimes  with  copper.     A  weighed  quantity  of  the  metal  to 
be  assayed  is  first  melted  with  about  three  times  its  weight  of  silver,  and  the 
resulting  button  is  cupelled  in  a  bone-ash  cupel  ($  433).     The  copper  and  any 
other  base  metals  present  are  so  converted  into  oxides,  which  are  absorbed  by 
the  cupel,  and  a  button  containing  only  gold  and  silver  is  obtained.     This  is 
hammered  out  into  a  thin  sheet,  which  is  twisted  up  and  boiled  in  nitric  acid ; 
the  silver  is  dissolved,  while   the  gold   remains  as  a  spongy  mass,  which  is 
washed,  heated  to  redness,  and  then  weighed. 

The  gold  coin  of  the  United  States  contains  90  per  cent,  of  gold,  the  re- 
mainder being  copper. 

505.  GILDING. — Silver  and  copper  objects  may  be  gilded  by  rubbing  over 
them  an  amalgam  of  gold  with  eight  times  its  weight  of  mercury.     They  are 
then  heated  under  a  chimney  so  arranged  that  the  poisonous  mercury  vapor 
may  be  entirely  carried  off.     The  dull  gilded  surface  is  then  rendered  brilliant 
by  burnishing.     A  thin  film  of  gold  is  deposited  on  copper  objects  when  they 
are  dipped  into,  a  hot  solution  of  auric  chloride  with  sodium  carbonate  and 
sodium  phosphate. 

Gilding  is  best  accomplished  by  connecting  the  objects  to  be  gilded  with  the 
zinc  pole  of  a  voltaic  battery,  and  immersing  them  in  a  solution  obtained  by 
boiling  auric  chloride  with  potassium  cyanide.  The  positive  pole  of  the  bat- 
tery is  connected  with  a  plate  of  gold  immersed  in  the  same  liquid. 

The  rare  elements  indium  and  thallium,  both  of  which  were  discovered  by 
the  aid  of  the  spectroscope,  are  related  to  gold  and  bismuth  in  the  general  con- 
stitution of  their  compounds.  Traces  of  indium  exist  in  most  zinc  blendes, 
while  small  quantities  of  thallium  occur  in  certain  iron  pyrites,  and  the  metal 
is  obtained  from  the  dust  which  collects  in  the  flues  of  sulphuric  acid  works 
when  these  pyrites  are  burned  for  the  production  of  sulphur  dioxide. 


ALUMINIUM.  301 

LESSON    LVIL 
ALUMINIUM.     Al  =  27.5. 

f  06.  Although  this  is  one  of  the  most  abundant  elements,  it 
is  f'tund  only  in  combination,  and  the- preparation  of  the  metal  is 
a  n  atter  of  much  difficulty.  It  is  made  by  throwing  a  mixture 
of  odium  and  double  chloride  of  aluminium  and  sodium  on  the 
red  hot  hearth  of  a  reverberatory  furnace  from  which  the  air  is 
excluded.  Aluminium  chloride  may  be  used  instead  of  the  double 
chic-ride  mentioned,  but  the  latter  is  more  easily  prepared,  and  is 
not  so  readily  altered  by  contact  with  air  as  the  former.  Some 
cry  >  lite  is  added  to  the  mixture  to  serve  as  a  flux.  The  reaction 
resi  Its  in  the  formation  of  sodium  chloride  and  aluminium. 

A12Cl6,2NaCl  +         3Na2       =       SNaCl     +     Al* 

Ainu  inium  and  sodium  double  chloride.  Aluminium. 

The  globules  of  aluminium  are  then  fused  together,  and  cast 
into  ingots. 

Aluminium  is  a  bluish-white  metal,  capable  of  being  highly 
policed.  It  is  very  ductile  and  malleable,  and  also  very  sonorous. 
It  is-  a  good  conductor  of  heat  and  electricity.  Its  density  is  2.56 ; 
it  is  therefore  as  light  as  glass  and  porcelain.  It  melts  at  about 
750°.  It  is  unaltered  by  the  air  at  ordinary  temperatures,  but 
when  melted  absorbs  oxygen  and  is  converted  into  aluminium 
oxide.  It  is  hardly  affected  by  either  nitric  or  sulphuric  acid, 
but  dissolves  readily  in  hydrochloric  acid,  disengaging  hydrogen 
and  forming  aluminium  chloride.  It  is  also  dissolved  by  boiling 
solutions  of  the  alkaline  hydrates,  hydrogen  being  set  free,  while 
alkaline  aluminates  are  formed. 

The  great  tenacity  of  aluminium,  and  its  lightness  and  un- 
changeableness  in  the  air,  render  it  an  exceedingly  valuable  metal, 
but  unfortunately  the  high  cost  of  its  production  has  prevented  its 
employment  for  many  purposes  to  which  it  is  admirably  adapted. 

26 


302 


LESSONS    IN    CHEMISTRY. 


Aluminium  is  a  tetratomic  metal,  but  the  molecules  of  its  com- 
pounds contain  two  atoms  of  aluminium,  which  together  form  a 
hexatomic  couple,  capable  of  combining  with  six  atoms  of  chlorine, 
three  of  oxygen,  etc. 

507.  ALUMINIUM  CHLORIDE,  APC16. — When  aluminium  or  its 
hydrate  is  dissolved  in  hydrochloric  acid,  a  solution  of  aluminium 
chloride  is  obtained,  but  this  solution  cannot  be  evaporated  to  dry- 
ness  without  decomposing  into  aluminium  oxide  and  hydrochloric 

acid. 

A12C16        +        3H20        =        A1203        +        6HC1 

Solid  aluminium  chloride  is  formed  by  passing  chlorine  gas  over 
a  red-hot  mixture  of  aluminium  oxide  and  charcoal,  which  has 
been  made  into  small  balls  with  a  little  oil,  and  then  calcined  in  a 
crucible.  These  balls  are  put  in  a  clay  tube  or  retort,  which  is 
heated  to  bright  redness,  and  dry  chlorine  is  then  passed  through 
(Fig.  120).  Carbon  monoxide  and  aluminium  chloride  are 


FIG.  120. 

formed,  and  the  latter,  being  volatile,  must  be  condensed  in  a  bottle 
surrounded  with  cold  water. 

+         30        +        3C12       =       SCO       H- 


A1203 
Aluminium  oxide. 


A12C16 
Aluminium  chloride. 


Aluminium  chloride  is  a  white  or  pale-yellow  crystalline  com- 
pound, which  melts  at  a  gentle  heat,  and  volatilizes  at  a  tempera- 
ture slightly  above  100°.  When  thrown  into  water,  it  dissolves 


ALUMINIUM    SULPHATE.  303 

and  combines  with  the  liquid,  forming  a  hydrate,  which  cannot  be 
dried  without  decomposition.  It  slowly  absorbs  moisture  from  the 
air,  giving  off  hydrochloric  acid  while  aluminium  oxide  is  formed. 
The  double  chloride  of  aluminium  and  sodium  which  is  used  in 
the  preparation  of  aluminium,  melts  at  about  200°  ;  it  is  made 
wlu  n  common  salt  is  added  to  the  mixture  of  aluminium  oxide 
and  charcoal  used  in  the  preparation  of  aluminium  chloride. 

508.  ALUMINIUM    OXIDE,  AFO3. — This  compound   is   com- 
moi  ly  called   alumina.     It  is  found  native  in  corundum,  ruby, 
sap]  'hire,  topaz,  and  emery :   the  black  color  of  the  latter  is  due 
to  t  ie  presence  of  oxide  of  iron.     Aluminium  oxide  may  be  ob- 
tained in  the  laboratory  by  heating  the  aluminium  hydrate  which 
is  t  irown  down  as  a  gelatinous  white  precipitate  when  ammonia 
is  a  Ided  to  a  solution  of  alum.     It  then  forms  a  white  powder, 
whi  ;h  is  infusible  except  at  the  temperature  of  the  oxy hydrogen 
blov-pipe  flame  ;  it  is  not  reducible  by  either  hydrogen  or  char- 
coal     The  crystallized  varieties  of  alumina  are  used   as  gems: 
rub    is  red,  sapphire  is  blue,  and  topaz  is  yellow.     By  reason  of 
thei  *  hardness,  corundum  and  emery  are  of  great  value  in  grinding 
and  polishing  glass,  steel,  and  metals. 

Aluminium  hydrate,  A12(OH)6,  forms  a  bulky  gelatinous  pre- 
cipitate when  ammonia-water  or  an  alkaline  hydrate  or  carbonate 
is  added  to  a  solution  of  alum  or  any  salt  of  aluminium. 

509.  ALUMINIUM  SULPHATE,  A12(S04/. — Clay  is  a  silicate  of 
alun  inium,  usually  colored  yellow  by  the  presence  of  a  little  iron. 
By  boiling  with  strong  sulphuric  acid,  clay  is  decomposed,  a  solu- 
tion of  aluminium  sulphate  being  formed.     This  body  is  made 
from  clay  as  free  as  possible  from  iron  ;  when  its  solution  is  evap- 
orated, a  white  crystalline  mass  is  obtained,  and  by  special  precau- 
tions the  salt  may  be  crystallized  in  small  pearly  scales  or  needles 
containing  eight  molecules  of  water  of  crystallization.     It  is  sol- 
uble in  twice  its  weight  of  cold  water,  and  is  used  as  a  mordant  in 
dyeing,  for  it  may  be  decomposed  in  the  fibres  of  the  tissues  to  be 
dyed,  and  the  fine  particles  of  aluminium  oxide  deposited  firmly 
fix  the  color  in  the  fabric.     For  this  purpose  it  is  usually  first  con- 
verted into  aluminium  acetate  by  the  addition  of  calcium  acetate. 


304  LESSONS    IN*  CHEMISTRY. 

When  aluminium  sulphate  is  heated,  it  first  loses  ito  water  of 
crystallization,  and  then  gives  off  sulphur  trioxide,  leaving  a  resi- 
due of  aluminium  oxide. 

A12(SO^  3SQ3  +  AFO3 

510.  ALUMS. — To  a  cold  saturated  solution  of  aluminium  sul- 
phate, we  add  a  cold  saturated  solution  of  potassium  sulphate,  and 
stir  the  mixture.  A  crystalline  deposit  forms.  The  two  salts 
have  combined  to  form  a  double  salt,  which  is  called  an  alum.  It 
crystallizes  with  twenty- four  molecules  of  water  of  crystallization, 
and  its  formula  is  A12(SO)3.K2S04  +  24H20.  By  the  substitu- 
tion of  sodium  sulphate  or  ammonium  sulphate  for  the  potassium 
sulphate  in  the  preceding  experiment,  sodium  alum  or  ammonium 
alum  will  be  formed.  The  compositions  of  these  substances  are 
precisely  analogous  to  that  of  the  potassium  alum,  and  they  crys- 
tallize in  the  same  form,  which  is  the  regular  octahedron. 

Al2(S04)3.Na2S04     +     24H20     Sodium  alum. 
A12(S04)3.(NH4)2S04     +     24H20     Ammonium  alum,  ordinary  alum. 

Potassium  alum  is  soluble  in  about  thirty  times  its  weight  of  cold  water,  and 
in  less  than  one-third  its  weight  of  boiling  water.  It  forms  voluminous,  trans- 
parent crystals  when  the  hot  saturated  solution  is  allowed  to  cool.  When 
heated,  it  melts  in  its  water  of  crystallization,  which  is  afterwards  driven  off; 
the  salt  increases  enormously  in  volume,  and  the  anhydrous  alum  then  forms 
a  white,  porous  mass.  Alum  may  be  obtained  crystallized  in  cubes  by  adding 
a  very  small  quantity  of  potassium  carbonate  or  hydrate  to  its  hot  solution  and 
allowing  it  to  cool. 

Sodium  alum  is  very  soluble  in  cold  water,  and  is  not  employed  in  the  arts. 

Ammonium  alum  is  the  compound  ordinarily  called  alum.  Its  solubility  is 
about  the  same  as  that  of  potassium  alum.  When  it  is  strongly  heated,  it 
leaves  a  residue  of  pure  alumina. 

Other  metals  whose  oxides  are  analogous  in  constitution  to  aluminium  oxide, 

form  alums  having  compositions  and  general  properties  like  those  of  ordinary 

alum.    These  alums  are  isomorphous.     Although  their  colors  be  different,  they 

may  be  mixed  in  the  same  crystal,  and   the  form   of  the  latter  will   remain 

unchanged.     Thus,  chromium  alum  is  red :   when  one  of  its  red  octahedral 

crystals  is  immersed  in  a  saturated  solution  of  potassium  alum  and  the  water 

is  allowed  to  evaporate,  the  octahedron  will  grow  larger,  and  the  red  chromium 

alum  will  be  surrounded  by  the  colorless  potassium  alum.     The  compositions 

of  three  of  these  alums  are  shown  by  the  following  formulae : 

Iron  alum,  Fe2(S04)3.K2S04       +     24I120 

Manganese  alum,  Mn2(S04j3.K2S04     +     24H20 

Chromium  alum,    Cr2(S04)3.K2S04       +     24H20 


CLAY    AND    POTTERY.  305 

Ml.  CLAY  AND  POTTERY. — Feldspar,  albite,  and  labradorite 
arc  double  silicates  of  aluminium  and  potassium,  sodium  and  cal- 
ciu  n,  respectively.  Granite  and  mica  are  also  double  silicates  of 
alu-ninium  with  the  alkaline  silicates  or  calcium  silicate.  The  dis- 
int''gration  of  these  rocks  by  the  action  of  air  and  frost  results 
in  he  formation  of  clays,  and  the  nature  of  a  clay  will  depend  on 
tha:  of  the  rock  from  which  it  is  derived.  The  purest  clay  is  a 
hy<  .rated  silicate  of  aluminium  known  as  kaolin,  or  porcelain  clay. 
It  'ontains  Al203.2Si02.2H20.  Clays" which  form  a  coherent  mass 
wh  >n  mixed  with  water,  and  which  when  calcined  become  very 
hai  1  without  being  fused,  are  called  plastic  clays,  and  are  used  for 
the  manufacture  of  bricks,  fire-brick,  pottery,  etc.  Fuller  s  earth 
is  ;  kind  of  clay  of  which  the  paste  is  not  strongly  coherent:  it  is 
use  1  in  scouring  and  fulling  cloths.  Marls  are  mixtures  of  clay 
am  chalk,  generally  of  a  greenish  color,  and  often  found  in  large 
dej  osits :  they  are  used  as  fertilizers  for  sandy  soils. 

::>orcelain  is  made  from  a  mixture  of  the  finest  kaolin  with  a 
litt  e  finely-powdered  sand  and  feldspar,  which  are  added  to  pre- 
vei  t  the  mass  from  shrinking  and  to  render  the  ware  translucent 
by  andergoing  partial  fusion.  The  greatest  care  is  exercised  that 
the  materials,  which  are  made  into  a  paste  with  water,  may  be 
intimately  mixed  ;  after  the  articles  have  been  fashioned  from  the 
perfectly  homogeneous  paste,  they  are  baked  at  a  dull  red  heat,  and, 
after  cooling,  are  removed  from  the  furnace.  They  are  then  dipped 
int(  water  holding  in  suspension  a  mixture  of  kaolin  and  quartz  in 
an  impalpable  powder.  This  powder  fills  the  pores  on  the  surface, 
and  when  the  articles  are  again  baked  the  mixture  fuses  and  forms 
a  transparent  glaze,  while  the  whole  mass  becomes  partially  vitrified. 

Stoneware  is  manufactured  from  a  kaolin  which  is  not  sufficiently 
pure  for  porcelain -making.  It  is  baked  at  one  operation,  and  when 
the  temperature  of  the  oven  is  very  high  a  little  common  salt  is 
thrown  on  the  incandescent  objects;  by  the  action  of  the  hydrogen 
compounds  in  the  flame,  hydrochloric  acid  is  formed,  while  the 
sodium  forms  a  double  silicate  with  aluminium  on  the  surface  of 
the  ware.  This  silicate,  being  quite  fusible,  melts  and  spreads  out 
on  the  surface  of  the  ware,  forming  an  even  glaze, 
u  26* 


306  LESSONS    IN    CHEMISTRY. 

Articles  of  faience  are  made  from  a  still  more  common  clay 
mixed  with  finely- powdered  quartz,  and,  after  being  rendered  cohe- 
rent by  a  preliminary  baking,  are  coated  with  a  mixture  of  pow- 
dered quartz,  potassium  carbonate,  and  lead  oxide.  This  mixture 
fuses  to  a  transparent  varnish  when  the  articles  are  baked  a  second 
time,  and  various  colors  are  obtained  by  the  addition  of  certain 
metallic  oxides.  Oxide  of  tin  renders  the  glaze  white  and  opaque. 

The  glazing  of  pottery  intended  for  culinary  purposes  should 
contain  no  lead,  as  lead  silicate  is  attacked  by  dilute  vegetable 
acids,  and  a  lead  salt  is  sometimes  so  formed  in  articles  of  food. 

512.  TESTS  FOR  ALUMINIUM. — Solutions  of  aluminium  salts 
usually  have  an  acid  reaction.  The  alkaline  hydrates  and  am- 
monia produce  gelatinous  white  precipitates  of  aluminium  hydrate, 
soluble  in  acids  and  in  the  alkaline  hydrates.  The  same  precipitate 
is  thrown  down  by  the  alkaline  carbonates  and  by  ammonium 
sulphide,  carbon  dioxide  being  liberated  by  the  former  and  hydro- 
gen sulphide  by  the  latter. 
A12(SO*)3  +  3(NH*)«S  +  3H2Q  =  A12(OH)6  +  3(NH4)2SO*  +  3WS 

When  an  aluminium  salt  or  aluminium  oxide  is  strongly  heated 
in  a  blow-pipe  flame,  and  the  resulting  white  mass  is  moistened 
with  a  drop  of  cobalt  nitrate  solution  and  again  heated,  it  be- 
comes sky-blue,  without  fusion. 

"513.  Closely  related  to  aluminium  by  chemical  analogies  arc  a  number  of 
rare  metals,  of  which  four  have  been  obtained  in  the  metallic  state.  They  are 
lanthanum,  cerium,  didyraium,  and  gallium.  The'  first  three  exist  as  sili- 
cates in  the  mineral  cerite  and  in  other  rare  minerals :  gallium  occurs  in  ex- 
ceedingly minute  quantities  in  certain  zinc  blendes. 

Scandium,  samarium,  holmium,  erbium,  thulium,  and  yttrium  are  elements 
which  have  not  been  obtained  in  the  metallic  state;  but  their  oxides  have  been 
isolated  in  small  quantities,  and  a  few  of  their  salts  have  been  studied.  Each 
of  these  elements  is  distinctly  characterized  by  a  peculiar  spectrum,  which  is 
an  unquestionable  indication  of  the  individuality  of  the  clement.  AH  these 
elements  appear  to  form  sesquioxides,  and  their  chlorides,  which  have  been 
prepared,  contain  two  atoms  of  metal  and  six  of  chlorine,  corresponding  in 
composition  to  aluminium  chloride. 


IRON    AND    ITS    METALLURGY.  307 


LESSON    LVIII. 
IRON  AND   ITS   METALLURGY. 

f  14.  Iron  is  found  in  the  metallic  state  in  meteoric  stones,  which 
are  occasionally  drawn  to  the  earth  during  its  passage  through  space. 

"he  more  important  iron  ores  are  ferroso-ferric  oxide,  Fe304, 
cal  jd  magnetic  iron  ore,  or  black  oxide  of  iron;  ferric  oxide, 
Fe  O3,  called  red  hematite;  ferric  hydrate  of  various  composition, 
kn<  wn  as  brown  hematite,  oolite,  goethite,  bog  iron  ore,  etc. ;  fcr- 
rons  carbonate,  FeCO3,  called  spathic  iron ;  and  iron  disulphide, 
FeS2,  which  is  iron  pyrites.  Excepting  in  comparatively  rare 
ca,<  is,  these  ores  are  mixed  'with  a  greater  or  less  proportion  of 
cla  ,  silicious  matters,  etc.  When  the  ore  contains  sulphur,  it  is 
firs  roasted,  and  the  sulphur  is  burned  into  sulphur  dioxide, 
wh  le  the  iron  remains  as  oxide.  The  sulphur  dioxide  produced 
by  '-he  roasting  of  pyrites  is  often  employed  in  the  manufacture 
of  sulphuric  acid. 

The  oxide  of  iron,  either  the  natural  ore  or  produced  by  the 
roasting,  is  reduced  by  being  heated  with  charcoal.  A  rather  primi- 
tive method,  but  one  which  for  ages  furnished  all  of  the  iron  em- 
ployed, and  which  is  still  used  for  the  reduction  of  very  rich  ores, 
is  known  as  the  Catalan  method,  the  name  being  derived  from 
the  Spanish  province  in  which  the  process  is  still  carried  on.  It 
consists  in  piling  the  ore  and  charcoal  in  two  heaps,  side  by  side, 
on  burning  charcoal  contained  in  the  hearth  of  a  furnace  where 
the  combustion  is  sustained  by  a  blast  of  air  from  the  tuyere  of  a 
bellows  (Fig.  121).  The  reduced  iron  collects  on  the  hearth  in  a 
spongy  mass,  which  is  removed  and  directly  submitted  to  the 
operation  of  forging.  The  silicious  matters  of  the  ore  combine 
with  a  portion  of  ferrous  oxide  produced  during  the  operation,  and 
form  a  very  fusible  slag,  consisting  of  ferrous  silicate. 

515.  The   blast -furnace  process  for  the  reduction   of  iron   is 


308 


LESSONS    IN    CHEMISTRY. 


applicable  to  all  iron  ores,  and  the  fuel  employed  is  either  char- 
coal, coke,  or  anthracite.  The  blast-furnace  is  a  tall  column  of 
considerable  height,  sometimes  almost  cylindrical,  but  more  often 

constructed  in  the  form  of  a 
double  frustum  of  cones  placed 
base  to  base  (Fig.  122).  It  is 
lined  with  infusible  fire-brick ; 
the  hearth  is  flat,  and  inclines 
very  slightly  towards  the  front, 
which  is  so  arranged  that  the 
molten  iron  may  be  drawn  off 
at  the  bottom  through  a  hole 
which  is  kept  closed  with  a  clay 
plug,  and  the  slag  may  be  re- 
moved as  it  accumulates  and 
floats  on  the  surface  of  the  liquid 
iron.  During  the  reduction,  the 
bottom  of  the  furnace  is  closed, 
and  a  blast  of  air  is  injected 
through  tuyere  pipes  (T)  by 
powerful  blowing  engines.  Coal, 

ore,  and  limestone  are  continually  supplied  in  alternate  layers  at  the 
open  top  of  the  furnace,  and  in  the  interval  between  the  introduc- 
tion of  these  materials  the  top  is  closed  by  a  conical  cap  or  dome, 
which  can  be  readily  moved  by  suitable  machinery.  At  the  be- 
ginning of  the  operation  the  furnace  is  heated  by  a  supply  of  com- 
bustibles only,  and,  when  the  temperature  has  been  sufficiently 
raised,  the  ore  and  limestone  are  gradually  alternated  with  the 
introduction  of  coal,  until  the  furnace  is  completely  filled.  By 
the  combustion  of  the  coal  immediately  above  the  tuyeres,  carbon 
dioxide  is  produced,  but  as  this  comes  in  contact  with  the  highly- 
heated  coal  it  is  reduced  to  carbon  monoxide :  as  the  latter  gas 
rises  through  the  mixture,  it  reduces  the  oxide  of  iron,  and  the 
metallic  iron  formed  is  disseminated  in  small  particles  through  the 
mass  of  reduced  ore.  As  the  materials  descend  in  the  furnace, 
the  silicious  matters  of  the  ore,  and  the  lime  resulting  from  the 


FIG.  121. 


BLAST-FURNACE    PROCESS. 


309 


action  of  the  heat  on  the  limestone,  unite  to  form  a  very  fusible 
slag  of  calcium  and  aluminium  silicate,  while  the  particles  of  iron 
are  igglomerated  together,  and,  together  with  the  slag,  flow  to  the 
health  of  the  furnace.  The  gases  produced  during  the  operation 
contain  a  large  proportion  of  carbon  monoxide;  they  are  carried 


FIG.  122. 

off  by  pipes  inserted  near  the  top  of  the  furnace,  and  their  com- 
bustion furnishes  heat  for  the  boilers  which  supply  steam  to  the 
blowing  engines  and  to  furnaces  containing  long  series  of  pipes, 
through  which  the  air  from  the  engines  is  forced  before  it  enters 
the  tuyeres.  The  blast  is  heated  as  highly  as  possible,  for  by  the 
use  of  hot  air  a  very  great  saving  is  effected  in  the  quantity  of 
fuel  required. 


310  LESSONS    IN    CHEMISTRY. 

When  a  sufficient  quantity  of  iron  has  accumulated  on  the 
hearth  of  the  furnace,  the  blowing  engines  are  slowed  or  stopped, 
and  by  picking  out  the  clay  plug  the  molten  iron  is  caused  to  flow 
into  semi-cylindrical  channels  in  sand  on  the  floor  of  the  casting- 
room.  Blows  from  a  sledge-hammer  detach  the  bars  of  iron  so 
formed  from  that  in  the  channel  from  which  the  moulds  are  filled, 
and  they  constitute  pig-iron. 

This  iron  contains  carbon  and  a  small  proportion  of  silicon  and 
traces  of  sulphur  and  phosphorus,  which  it  has  removed  from  the 
materials  in  the  blast-furnace.  These  impurities  are  in  great  part 
removed  by  melting  the  iron  in  puddling-furnaces,  where  the 
carbon  and  silicon  are  oxidized  either  by  air,  or  better  by  oxygen 
derived  from  pure  magnetic  iron  ore,  or  from  scales  of  black  oxide 
of  iron  obtained  in  another  operation.  During  the  process,  the 
molten  iron  is  vigorously  stirred  until  it  is  converted  into  a  spongy 
mass,  which  is  then  removed  and  placed  under  a  steam-hammer, 
by  the  blows  of  which  all  the  ferrous  silicate  and  black  oxide  of 
iron  formed  during  the  process  of  puddling  are  squeezed  out,  while 
a  bloom  of  soft  iron  remains.  The  ferruginous  scoriae  or  ashes 
obtained  in  this  operation  are  used  in  refining  a  new  quantity  of 
cast-iron. 

516.  The  soft  iron  of  commerce,  called  forged  or  bar  iron,  is 
not  perfectly  pure.  It  contains  traces  of  carbon,  silicon,  sulphur, 
phosphorus,  nitrogen,  and  sometimes  other  elements.  Pure  iron 
may  be  obtained  by  passing  hydrogen  over  pure  ferric  chloride 
heated  to  bright  redness  in  a  porcelain  tube.  Hydrochloric 
acid  is  disengaged,  and  the  iron  remains  as  an  almost  infusible, 
spongy  mass.  By  passing  dry  hydrogen  over  ferric  oxide  heated 
to  dull  redness  in  a  glass  bulb  (Fig.  123),  metallic  iron  is  ob- 
tained as  a  dull  black  powder,  in  which  form  it  becomes  oxidized 
with  great  readiness.  If  a  lighted  match  be  applied  to  a  single 
point  in  recently -prepared  iron  reduced  by  hydrogen,  the  whole 
mass  quickly  takes  fire  and  burns  into  ferric  oxide.  By  reducing 
the  ferric  oxide  at  a  temperature  below  redness,  a  powder  of 
iron  may  be  obtained  which  will  even  take  fire  spontaneously  on 
contact  with  the  air. 


STEEL. 


311 


The  composition  and  general  properties  of  cast-iron  vary 
greatly,  for  while  cast-iron  always  contains  silicon  and  carbon, 
these  elements  do  not  appear  to  be  chemically  combined  with 
the  iron.  The  proportion  of  carbon  varies  from  2  to  5.5  per  cent. 
Wl  en  cast-iron  containing  a  large  proportion  of  carbon  is  rapidly 
coo  ed,  it  becomes  hard  and  brittle,  and  its  fracture  is  coarse,  crys- 
tall  ne,  and  very  white.  It  is  called  white  iron.  When,  however, 
sue  i  iron  is  allowed  to  cool  slowly,  a  considerable  quantity  of  the 

0 


FIG.  123. 

carbon  separates  as  shining  scales  of  graphite,  and  the  iron  is  then 
softer,  has  a  closer  structure,  and  a  gray  fracture.  It  is  called 
gray  iron.  Iron  containing  sulphur  and  phosphorus  is  always 
white;  phosphorus  renders  iron  brittle  while  cold,  and  sulphur 
renders  it  brittle  while  hot.  In  the  first  case  the  iron  is  said  to 
be  cold- short,  while  in  the  second  it  is  called  red-short. 

Kpiegeleisen,  or  looking-glass  iron,  is  a  variety  of  cast-iron  very 
rich  in  carbon,  and  containing  also  manganese ;  it  is  employed 
in  the  manufacture  of  steel ;  it  is  crystalline,  and  breaks  with 
smooth  and  highly-lustrous  surfaces. 

517.  Steel  is  iron  containing  from  0.2  to  2  per  cent,  of  carbon, 
and  traces  of  nitrogen.  It  is  obtained  by  a  number  of  processes, 
which  depend  either  on  the  partial  decarbonization  of  cast-iron  or 
on  the  introduction  of  the  required  proportion  of  carbon  into  soft 


312 


LESSONS    IN    CHEMISTRY. 


iron.  When  manganiferous  cast-iron  is  maintained  for  a  time 
melted  under  a  layer  of  magnetic  iron  ore  or  ferruginous  scoriae, 
and  the  operation  is  arrested  at  the  proper  moment,  the  iron  still 
retains  a  certain  proportion  of  carbon,  and  natural  steel  is  obtained. 
Cement-steel,  or  blister-steel,  is  made  by  piling  soft-iron  bars 
between  layers  of  charcoal  in  fire-clay  boxes,  which  are  then 
heated  to  redness  in  a  furnace,  and  the  temperature  is  maintained 
for  several  days  ;  the  iron  absorbs  a  certain  proportion  of  carbon, 
and  is  converted  into  steel.  As,  however,  the  exterior  of  the  bars 
will  necessarily  contain  more  carbon  than  the  interior,  the  metal 
is  rendered  homogeneous  by  being  melted  in  crucibles  heated  in  a 
powerful  wind-furnace.  It  then  constitutes  cast-steel. 

The  most  important  method  of  manufacture  of  steel  is  named, 
from  its  inventor,  the  Bessemer  process.  It  consists  in  completely 
decarbonizing  cast-iron  and  then  adding  sufficient  cast-iron  of  the 
proper  quality  to  give  to  the  whole  mixture  the  desired  proportion 
of  carbon.  The  operation  is  conducted  in  oval  vessels  of  strong 

iron  plate  lined  with  infusi- 
ble fire-brick.  This  appa- 
ratus, which,  is  called  a 
converter,  is  supported  on 
trunnions,  so  that  it  may 
swing  back  and  forward  on 
a  horizontal  axis.  One  of 
the  trunnions  is  hollow,  and 
communicates  with  a  pipe 
passing  partly  around  the 
converter  and  then  leading 
to  its  bottom  ;  the  fire-brick 
is  here  pierced  with  a 
number  of  holes,  so  that  a 
blast  of  air  may  be  forced 

FIG.  124.  UP  through  the  contents  of 

the   converter    (Fig.  124). 

The  plant,  as  the  whole  of  any  manufactory  is  called,  is  established 
near  blast-furnaces,  and  cupola  furnaces,  for  melting  the  pig-iron, 


BESSEMER  STEEL  PROCESS.  313 

are  constructed  near  the  converter.  Everything  being  ready, 
burning  wood  is  thrown  into  the  converter,  which  is  then  partly 
filled  with  coke,  and  the  blast  is  turned  on  so  that  the  fire-brick 
linhg  is  heated  to  whiteness.  The  converter  is  then  inverted; 
the  coke  is  dumped  out,  and  molten  iron  is  run  in  from  cupola 
fur  laces.  During  the  filling,  the  converter  is  kept  in  an  inclined 
pos.tion,  so  that  the  tuyeres  for  the  passage  of  the  blast  may  not 
bee  jme  filled  with  the  molten  iron.  The  blast,  which  is  under 
stT'  ng  pressure,  is  now  turned  on,  .and  the  converter  is  rotated 
to  n  upright  position.  As  the  air  bubbles  up  through  the  iron, 
the  carbon,  silicon,  and  other  oxidizable  elements  present  are  con- 
sui  led,  and  a  brilliant  flame  rushes  with  a  roaring  noise  from  the 
mo  ith  of  the  converter.  When  the  carbon  of  the  iron  is  burned 
out ,  the  appearance  of  the  flame  undergoes  a  change  which  informs 
the  workmen  of  the  termination  of  the  operation.  The  converter 
is  i  hen  inclined,  and  the  blast  is  arrested.  In  the  mean  time,  the 
quantity  of  iron  in  the  charge  being  accurately  known,  the  exact 
qu;  ntity  of  spiegeleisen  required  to  convert  this  charge  into  steel, 
ha;«  been  melted  in  another  cupola  furnace ;  as  soon  as  the  blast  is 
stopped,  this  molten  spiegeleisen  is  run  into  the  converter,  which 
is  ;  gitated  backward  and  forward  in  order  that  the  contents  may 
be  perfectly  mixed.  The  steel  is  then  poured  out  into  an  enor- 
mous ladle,  which  is  carried  by  a  revolving  crane  over  the  cir- 
cumference of  a  circle  around  which  are  arranged  ingot-moulds, 
intc  which  the  steel  is  cast.  The  motions  of  the  converter  and 
of  the  crane,  and  the  opening  and  closing  of  the  blast,  are  effected 
from  a  distance  by  means  of  hydraulic  machinery. 

518.  The  valuable  qualities  of  steel  depend  upon  the  ease  with 
which  it  can  be  hardened  or  softened  at  pleasure,  and  the  opera- 
tions by  which  the  change  in  hardness  is  brought  about,  consti- 
tute the  processes  of  tempering.  When  heated  and  allowed  to 
cool  slowly,  steel  becomes  soft  and  malleable  like  soft  iron,  but  if 
it  be  heated  to  redness  and  then  suddenly  cooled  by  plunging  it 
into  cold  water,  it  is  rendered  hard  and  brittle ;  it  is,  however, 
still  elastic.  When  steel  is  to  be  hardened,  it  must  either  be  ren- 
dered exceedingly  hard  and  brittle  by  rapid  cooling,  or  allowed  to 
o  27 


314  LESSONS    IN    CHEMISTRY. 

become  soft  by  slow  cooling.  Intermediate  degrees  of  hardness 
are  obtained  by  re-heating  hard  steel  to  temperatures  depending  on 
the  desired  hardness.  Part  of  the  temper  is  then  said  to  be 
drawn.  The  color  which  the  surface  of  the  metal  assumes  is  an 
index  of  the  temperature. 

Straw  yellow  corresponds  to  220°. 
Brown  "  255°. 

Light  blue  "  285-290°. 

Indigo  blue  "  295°. 

Sea  green  331°. 

When  a  number  of  small  objects  are  to  be  tempered  alike,  they 
are  heated  in  a  bath  of  mercury  or  oil,  of  which  the  temperature 
earn  be  exactly  regulated. 

We  may  very  well  study  the  phenomena  of  tempering  by  heat- 
ing a  steel  wire  or  a  piece  of  watch-spring  to  redness  and  quickly 
immersing  it  in  water.  It  is  now  very  hard  and  brittle  ;  it  breaks 
as  readily  as  a  piece  of  glass.  We  again  heat  it  gently  until  its 
surface  becomes  of  a  blue  color,  and  now,  whether  we  dip  it  in 
water  or  allow  it  to  cool  slowly,  we  will  find  that  it  has  become 
quite  elastic,  but  is  still  hard.  When,  however,  we  heat  it  to  red- 
ness and  allow  it  to  cool  slowly,  it  becomes  soft  and  flexible ;  it 
will  not  break,  but  will  retain  any  form  into  which  it  is  bent. 

The  process  of  casehardening,  which  is  applied  to  inferior 
kinds  of  cutlery,  consists  in  embedding  the  objects,  which  are 
made  of  soft  iron,  in  charcoal  contained  in  crucibles  or  clay  boxes. 
These  are  then  heated  to  bright  redness,  and  the  surface  of  the 
iron  becomes  converted  into  steel. 

Steel  is  less  fusible  than  cast-iron,  but  much  more  fusible  than 
soft  iron ;  at  the  temperature  at  which  soft  iron  becomes  pasty, 
steel  melts. 


IRON   AND    ITS   COMPOUNDS.  315 

LESSON    LIX. 
IRON  AND  ITS  COMPOUNDS. 

•  )19.  The  density  of  soft  iron  varies  from  7.4  to  7.9.  It  is 
du  tile,  malleable,  and  very  tenacious.  It  fuses  only  at  the  highest 
tei  iperatures  of  a  powerful  wind-furnace,  but  at  a  high  white 
he;  t  it  becomes  so  soft  that  two  pieces  of  the  metal  may  be  readily 
un  ted  in  a  solid  mass  by  hammering  or  by  pressure:  the  opera- 
tion is  called  welding.  At  a  somewhat  lower  temperature  it  may 
be  readily  rolled  into  sheets  or  bars,  and  sheet-iron  is  made  by 
pacing  the  heated  metal  between  polished  steel  rollers.  Iron  may 
be  rolled  into  leaves  as  thin  as  paper.  Tin  plate  is  sheet-iron 
co\  ered  with  a  coating  of  tin.  Galvanized  iron  is  made  by  dipping 
perfectly  clean  sheet-iron  into  melted  zinc. 

[ron  is  attracted  by  a  magnet,  and  becomes  itself  a  magnet 
while  under  the  magnetic  influence,  but  loses  its  magnetism  when 
tin  exciting  cause  is  removed.  Under  the  same  circumstances 
ste  3!  becomes  a  permanent  magnet. 

Unless  in  a  state  of  fine  division,  iron  is  unaffected  by  dry  air 
at  temperatures  below  redness,  but  at  a  red  heat  it  combines  with 
oxvgen  and  is  converted  into  a  black  oxide  which  forms  scales  on 
its  surface.  It  is  rapidly  rusted  by  moist  air,  and  the  rust  is  a 
hydrated  ferric  oxide. 

When  the  formation  of  rust  has  begun,  it  proceeds  with  great  rapidity,  and 
if  the  mass  of  iron  be  of  such  a  form  that  a  large  surface  is  combined  with  a 
comparative!}7  small  bulk,  as  in  a  long  coil  of  wire  or  mass  of  small  scrap  iron 
partly  immersed  in  water,  the  temperature  may  be  much  elevated  by  the  rust- 
ing. It  appears  that  hydrogen  dioxide  is  formed  during  the  rusting  of  iron,  and 
that  substance  would  greatly  accelerate  the  change:  the  nitrogen  of  the  air 
also  plays  some  part  in  the  phenomenon,  for  rust  always  contains  a  trace  of 
ammonia. 

At  a  red  heat,  iron  decomposes  water,  liberating  hydrogen,  and 
forming  an  oxide.  It  is  dissolved  by  hydrochloric  and  sulphuric 
acids,  hydrogen  being  set  free ;  this  hydrogen  has  an  unpleasant 


316  LESSONS    IN    CHEMISTRY. 

odor,  probably  due  to  carbon  compounds  formed  by  the  action 
of  the  carbon  of  the  iron.  Dilute  nitric  acid  also  dissolves  iron, 
disengaging  red  vapors,  but  the  strongest  nitric  acid  does  not 
affect  it. 

If  some  clean  iron  wire  or  some  bright  nails  be  dropped  into  pure  nitric  acid, 
or  a  mixture  of  strong  nitric  and  sulphuric  acids,  no  action  takes  place:  the 
iron  may  now  be  removed  and  placed  in  more  dilute  acid,  and  even  here  it 
will  not  dissolve:  it  is  said  to  be  in  the  passive  state.  Its  surface  has  become 
covered  with  a  protecting  layer  of  gas  derived  from  the  strong  acid :  if  while 
the  passive  iron  is  immersed  in  the  dilute  acid  we  touch  its  surface  with  a 
copper  wire,  the  coating  of  gas  is  broken  at  one  point,  chemical  action  is  at 
once  re-established,  and  the  iron  is  quickly  dissolved. 

Iron  forms  two  series  of  compounds,— ferric  compounds,  which 
are  analogous  to  those  of  aluminium,  and  in  which  two  tetratomic 
atoms  pass  from  molecule  to  molecule  as  a  hexatomic  couple,  and 
ferrous  compounds,  in  which  it  is  more  convenient  to  consider  the 
iron  atom  as  diatomic. 

520.  FERROUS  CHLORIDE,  FeCl2,  is  made  by  passing  dry  hydro- 
chloric acid  gas  over  metallic  iron  heated  to  redness  in  a  porcelain 
tube.      It  then  condenses  in  white,  pearly  scales  in  the  cooler  part 
of  the  tube. 

A  solution  of  ferrous  chloride  may  be  obtained  by  dissolving  iron  in  hydro- 
chloric acid.  When  the  filtered  liquid  is  sufficiently  evaporated,  it  deposits 
bluish-green  crystals  in  which  every  molecule  of  ferrous  chloride  is  combined 
with  four  molecules  of  water. 

521.  FERRIC  CHLORIDE,   Fe2Cl6,  sublimes  in  brilliant  violet 
crystals  when  chlorine  is  passed  over  incandescent  iron  contained 
in  a  glass  or  porcelain  tube.     It  is  very  soluble  in  water,  but  its 
solution  undergoes  a  curious  change  by  boiling.     A  solution  of 
ferric  chloride  is  obtained  by  dissolving  ferric  oxide  or  powdered 
hematite  in  hot  hydrochloric  acid.     When  this  solution  is  evapo- 
rated at  a  low  temperature,  the  hydrated  ferric  chloride  remains  as 
a  brownish-yellow,  deliquescent  mass,  but  when  the  solution  is 
boiled  its  color  darkens,  and  the  reactions  and  general*  properties 
of  the  liquid  seem  to  show  that  it  has  been   decomposed   into 
hydrochloric  acid  and  a  soluble  variety  of  ferric  hydrate. 

522.  FERROUS  OXIDE,  FeO,  has  been  obtained  as  a  black  powder  by  passing 


OXIDES   OF    IRON.  317 

a  mixture  of  carbon  dioxide  and  carbon  monoxide  in  equal  volumes  over  heated 
ferric  oxide.     Carbon  monoxide  alone  would  yield  metallic  iron. 

523.  FERRIC  OXIDE,  Fe203,  constitutes  the  minerals  known  as 
red  hematite  and  specular  iron.    It  is  obtained  as  a  fine  red  powder 
by  strongly  heating  ferrous  sulphate  in  a  crucible  :  sulphur  dioxide 
ai  d  sulphur  trioxide  are  disengaged,  while  ferric  oxide  remains. 

2FeS04     =     SO2     +     SO3     +     Fe203 

T  iis  powder  is  very  hard,  and  is  used  for  polishing  under  the 
n  <mes  jewellers'  rouge  and  colcolhar. 

When  an  alkaline  hydrate  or  ammonia  is  added  to  a  solution  of 
f(  rric  chloride,  a  flocculent,  brown  precipitate  of  ferric  hydrate, 
F32(OH)6,  is  thrown  down.  This  is  the  precipitate  which,  after 
b  ing  thoroughly  washed,  is  the  proper  antidote  for  poisoning  by 
u'i  seuious  oxide.  Ferric  solutions  containing  tartaric  acid  are  not 
p  ecipitated  by  the  alkaline  hydrates. 

Rust  is  a  ferric  hydrate  of  which  the  composition  usually  corresponds  with 
tie  formula  (Fe203)23H20  =  Fe'2(OH)6  +  Fe203.  This  is  also  the  composition 
ol  the  natural  hydrate  brown  hematite.  Goethite  is  a  hydrate  having  the 
composition  Fe203.H20  =  Fe2(OH)20. 

There  is  a  soluble  modification  of  ferric  hydrate.  It  may  be  obtained  by 
pi  uring  a  solution  of  ferric  chloride  which  has  been  heated  to  100°  into  the 
inner  vessel  of  a  dialyser  (§  220),  the  water  in  the  exterior  vessel  being  fre- 
quently changed.  Hydrochloric  acid  passes  through  the  membrane,  while  a 
solution  of  ferric  hydrate  remains  within.  Dialysis  of  a  solution  of  ferric 
ac  etate  yields  soluble  ferric  hydrate  in  the  same  manner.  This  solution  is 
u.-ed  in  medicine  under  the  name  dialysed  iron. 

524.  FERROSO- FERRIC  OXIDE,  Fe30*,  is  magnetic  oxide  of  iron, 
commonly  called  black  oxide  of  iron.     It  is  found  native  in  large 
quantities  in  the  neighborhood  of  Lake  Superior.     It  forms  in 
black  scales  on  the  surface  of  iron  heated  to  redness  in  the  air.     It 
is  attracted  by  the  magnet.    It  is  a  compound  of  ferrous  and  ferric 
oxides,  Fe304  =  FeO.Fe203. 

525.  FERROUS  SULPHIDE,  FeS,  so  largely  used  in  the  labora- 
tory for  the  preparation  of  hydrogen  sulphide,  is  made  by  heating 
a  mixture  of  iron  filings  with  two-thirds  its  weight  of  sulphur  to 
redness  in  a  covered  crucible.     After  fusion,  the  mass  is  poured 
out,  and  on  cooling  forms  a  black  solid  of  a  metallic  appearance. 

526.  IRON  DISULPHIDE,  FeS2,  constitutes  the  common  mineral 

27* 


318  LESSONS   IN    CHEMISTRY. 

iron  pyrites.  It  is  dimorphous,  being  found  in  cubical  crystals  of 
a  yellow  color  and  metallic  lustre,  known  as  yellow  pyrites ;  and  as 
rhombic  prisms  of  a  pale,  greenish-yellow  color,  constituting  white 
pyrites.  When  pyrites  is  heated  in  closed  vessels,  part  of  its  sul- 
phur distils ;  when  it  is  heated  in  contact  with  air,  the  sulphur 
burns  into  sulphur  dioxide,  while  the  iron  remains  as  oxide.  The 
brilliant  metallic  appearance  of  iron  pyrites  has  sometimes  caused 
it  to  be  mistaken  for  gold,  and  it  has  been  called  fool's  gold  :  the 
action  of  heat  at  once  reveals  its  true  character. 

527.  FERRIC    SULPHATE,    Fe2(S04)3. — Ferrous   sulphate,   or 
green  vitriol,  has  already  been  described  (§  123)  :  when  crystals 
of  this  salt  are  dissolved  in  water,  and  boiled  with  a  little  less  than 
one-sixth  their  weight  of  sulphuric  acid,  and  small  quantities  of 
nitric  acid  are  added  from  time  to  time,  a  solution  of  ferric  sul- 
phate is  obtained.     When  this  liquid  is  evaporated  to  dryness, 
ferric  sulphate  remains  as  a  yellowish-white  mass,  very  soluble  in 
water.     By  using  a  smaller  quantity  of  sulphuric  acid,  various 
basic  salts  are  obtained,  and  they  may  be  considered  as  ferric  sul- 
phate in  which  one  or  two  groups,  SO4,  are  replaced  by  as  many 
atoms  of  oxygen.     Such  are  Fe20(S04)2  and  Fe202S04.     A  mix- 
ture of  these  basic  sulphates  is  employed  in  medicine  under  the 
name  Monsel's  solution.     It  is  astringent  and  styptic,  and  is  valu- 
able for  arresting  hemorrhage. 

528.  TESTS  FOR  IRON. — The  ferrous  and  the  ferric  salts  are 
characterized  by  different  reactions ;  by  reducing  agents  such  as 
nascent  hydrogen  produced  by  zinc  and  hydrochloric  acid,  the  ferric 
salts  are  converted  into  ferrous  salts,  while  ebullition  with  nitric 
acid,  or  the  addition  of  chlorine- water,  will  produce  a  ferric  com- 
pound from  a  ferrous  salt. 

Solutions  of  the  ferrous  salts  are  pale  green  ;  hydrogen  sulphide 
occasions  in  them  no  precipitate,  but  ammonium  sulphide  throws 
down  black  ferrous  sulphide.  The  alkaline  hydrates  and  ammonia 
produce  greenish-white  precipitates  of  ferrous  hydrate  which  rap- 
idly become  dark  by  absorbing  oxygen  from  the  air.  Potassium 
ferrocyanide  forms  a  pale-blue  precipitate ;  potassium  ferricyanide 
occasions  a  dark-blue  precipitate,  called  Turnbull's  blue. 


COBALT.  319 

Isolations  of  ferric  salts  are  yellowish-brown  or  brown.  With 
hydrogen  sulphide  they  yield  a  precipitate  of  sulphur,  being 
reduced  to  ferrous  salts  ;  ammonium  sulphide  throws  down  a 
black  precipitate.  The  alkaline  hydrates  and  ammonia  form  rust- 
cokred  precipitates  of  ferric  hydrate,  insoluble  in  an  excess  of  the 
reai  ent.  Potassium  ferrocyanide  throws  down  Prussian  blue ; 
poti.ssium  ferricyanide  occasions  no  precipitate.  Potassium  sul- 
phojyauate  produces  a  blood-red  color,  due  to  the  formation  of 
feri  ic  sulphocyanate.  Tannin,  or  an  infusion  of  gall-nuts,  forms 
a  bl  le-black  and  very  finely  divided  precipitate,  which  long  remains 
sus]  ended  in  the  liquid. 


LESSON    LX. 

COBALT,  NICKEL,  AND    MANGANESE. 

5  39.  Cobalt,  Co  =  59. — This  metal  is  found  combined  with 
sulp  mr  and  arsenic  ;  the  mineral  cobaltine  is  a  sulpharsenide  of 
cobalt,  having  the  composition  CoSAs.  Metallic  cobalt  is  obtained 
by  s ':rongly  heating  with  a  little  charcoal  in  a  covered  crucible  the 
cobalt  oxalate,  which  is  precipitated  by  the  addition  of  ammonium 
oxal;ite  to  the  solution  of  a  cobalt  salt.  Carbon  dioxide  is  disen- 
gage!, while  cobalt  remains  as  a  dull  powder,  which  may  be  fused 
into  a  button  by  the  highest  heat  of  a  wind-furnace.  It  is  a 
silvery- white  metal,  and  is  malleable  and  ductile.  It  is  attracted 
by  the  magnet.  Its  density  is  8.6.  It  is  unaffected  by  either 
dry  or  moist  air  at  ordinary  temperatures,  but  is  oxidized  at  a 
red  heat. 

Cobalt  forms  cobaltous  oxide,  CoO,  a  sesquioxide,  Co203,  and  several  other 
oxides  which  appear  to  be  formed  by  a  combination  of  these  two  in  different 
proportions. 

530.  COBALT  CHLORIDE,  CoCl2,  is  prepared  by  dissolving  either  the  oxide  or 
carbonate  of  cobalt  in  hydrochloric  acid.  The  solution  is  red,  and,  when  con- 
centrsited,  deposits  red  crystals  containing  six  molecules  of  water  of  crystalli- 
zation. Anhydrous  cobalt  chloride  is  blue  :  if  a  little  strong  sulphuric  or 
hydrochloric  acid  be  added  to  a  concentrated  solution  of  cobalt  chloride,  the 


320  LESSONS    IN    CHEMISTRY. 

liquid  becomes  blue.  It  contains  anhydrous  cobalt  chloride.  Writing  mads 
on  paper  with  a  very  dilute  solution  of  cobalt  chloride  is  invisible  when  dry  ; 
the  small  quantity  of  the  salt  present  is  hydrated  ;  but  if  the  paper  be  heated, 
the  characters  become  blue,  for  the  water  is  driven  off.  After  exposure  to  the 
air  for  a  time,  the  characters  again  fade,  the  cobalt  chloride  absorbing  atmos- 
pheric moisture. 

531.  COBALT  BLUE. — The  ores  of  cobalt  are  principally  em- 
ployed for  the  manufacture  of  a  dark-blue  substance  generally 
called  smalt.  This  is  a  mixture  of  cobalt  silicate  and  potassium 
silicate.  It  is  prepared  by  partially  roasting  the  ore  in  order  to 
convert  the  greater  part  of  the  cobalt  into  oxide.  The  roasted 
mass  is  then  pulverized  and  melted  with  a  mixture  of  potassium 
carbonate  and  white  quartz  sand.  A  blue,  vitreous  mass  is  thus 
obtained,  which  floats  on  a  fused  mass  containing  the  iron,  nickel, 
copper,  and  unaltered  sulphur  and  arsenic  of  the  ore.  This  mix- 
ture has  a  metallic  appearance  ;  it  is  called  speiss,  and  is  used  for 
the  preparation  of  nickel.  While  still  molten,  the  blue  glass  con- 
stituting smalt  is  poured  into  water,  in  which  it  breaks  up  into 
small  fragments,  which  are  readily  pulverized. 

An  impure  sesquioxide  of  cobalt  is  used  for  painting  on  glass 
and  porcelain,  to  which  it  communicates  a  deep-blue  color. 

532.  TESTS  FOR  COBALT. — The  more  ordinary  salts  of  cobalt  form  rose- 
colored  or  currant-red  solutions,  but  if  these  solutions  contain  free  acid,  they 
become  blue  when  heated.  They  are  not  precipitated  by  hydrogen  sulphide; 
ammonium  sulphide  forms  a  black  precipitate.  The  alkaline  hydrates  pro- 
duce blue  precipitates,  which  an  excess  of  the  reagent  converts  into  rose- 
colored  cobaltous  hydrate,  Co(OH)2.  Ammonia-water  occasions  a  blue  pre- 
cipitate, which  dissolves  in  an  excess  of  the  reagent,  an  ammonio-cobalt  salt 
being  formed.  When  strongly  heated  with  a  little  borax  on  the  end  of  a 
platinum  wire,  the  compounds  of  cobalt  yield  beads  of  a  blue  glass. 

533.  Nickel,  Ni  =  59.— Nickel  is  found  principally  as  ar- 
senide, NiAs2,  in  the  mineral  kupfernickel,  which  is  generally  as- 
sociated with  ores  of  copper  and  iron.  It  is  obtained  from  this 
mineral  and  from  the  speiss  formed  during  the  manufacture  of 
smalt.  The  speiss  or  kupfernickel  is  first  roasted,  in  order  that 
the  nickel  may  be  converted  into  oxide,  and  is  afterwards  heated 
with  powdered  charcoal  as  long  as  arsenic  vapors  are  disengaged. 
The  mass  is  then  dissolved  in  nitro-hydrochloric  acid,  and  the  so- 
lution is  evaporated  to  expel  the  excess  of  acid.  Hydrogen  sul- 


NICKEL.  321 

phide  is  passed  through  the  liquid  as  long  as  it  occasions  any  pre- 
cipiiate,  and  all  the  metals  present  excepting  iron,  nickel,  and 
cobalt  are  thus  precipitated  as  sulphides.  The  addition  of  sodium 
carbonate  to  the  clear  decanted  liquid  precipitates  the  iron,  nickel, 
and  cobalt.  The  mixed  precipitate  is  washed  and  treated  with 
oxalic  acid  and  an  excess  of  ammonia- water.  An  ammoniacal 
solu  ion  of  the  oxalates  of  nickel  and  cobalt  is  so  obtained  ;  this  is 
exp<  sed  to  the  air,  and  as  the  ammonia  gradually  volatilizes,  the 
nick  el  oxalate  is  first  deposited  in  greenish  crystals,  after  which 
the  :obalt  oxalate  separates.  The  precipitates  are  removed  from 
day  to  day,  and  the  nickel  salt  is  several  times  dissolved  in  am- 
moii  ia,  and  allowed  to  separate  until  it  is  free  from  cobalt.  It  is 
thei  treated  with  an  alkaline  hydrate,  and  the  resulting  nickel 
hyd  ate  is  dried,  mixed  with  charcoal  powder  and  oil,  and  the 
past  !  thus  obtained  is  calcined  at  the  highest  temperature  of  a 
goo(  furnace.  The  reduced  nickel  then  fuses  and  forms  a  mass. 

N  ickel  may  be  prepared  in  the  laboratory  by  strongly  heating 
its  o  talate  out  of  contact  with  the  air. 

N.'ckel  is  a  yellowish-white  metal,  capable  of  taking  a  high  polish. 
It  is  nalleable,  ductile,  and  very  tenacious.  Its  density  is  about  8.5. 
It  is  attracted  by  the  magnet.  It  is  the  hardest  of  the  more  common 
metals.  It  is  not  affected  by  the  air  at  ordinary  temperatures,  but 
becomes  oxidized  at  a  red  heat.  It  is  slowly  dissolved  by  dilute 
hydrochloric  and  sulphuric  acids,  more  rapidly  by  nitric  acid. 

Nickel  is  employed  in  the  manufacture  of  a  number  of  alloys. 
German  silver  contains  25  per  cent,  of  nickel,  25  per  cent,  of 
zinc,  and  50  per  cent,  of  copper,  but  the  proportions  vary  greatly. 
The  white  nickel  coins  of  the  United  States  contain  25  per  cent, 
of  nickel  and  75  per  cent,  of  copper. 

Nickel  is  largely  employed  for  plating  articles  of  brass,  iron, 
and  steel,  and  its  hardness,  its  high  lustre,  and  its  freedom  from 
rust  render  it  admirably  adapted  to  this  purpose.  The  well- 
cleaned  objects  are  attached  to  the  zinc  pole  of  a  voltaic  battery 
and  immersed  in  a  solution  of  nickel  and  ammonium  double 
sulphate :  the  positive  pole  of  the  battery  is  connected  with  a 
plate  of  pure  nickel  dipped  in  the  same  liquid. 


322  LESSONS    IN    CHEMISTRY. 

534.  NICKEL  CHLORIDE,  NiCl2,  is  made  by  dissolving  the  oxide  or  hydrate 
in   hydrochloric  acid.      When    sufficiently  concentrated,   the  green   solution 
deposits  green  crystals  containing  NiCl2  +  6H20. 

535.  NICKEL  MONOXIDE,  NiO,  is  a  pale-gray  powder,  obtained  by  strongly 
heating  the  carbonate  or  nitrate.     Nickel  hydrate,  Ni(OH)2,  is  thrown  down 
as  a  pale-green  precipitate  when  an  alkaline  hydrate  is  added  to  the  solution 
of  a  nickel  salt.     When  chlorine  is  passed  through  water  in  which  this  pre- 
cipitate is  suspended,  a  hydrate  of  nickel  sesquioxide,  Ni'203,  is  formed. 

536.  NICKEL  SULPHATE,  NiSO4. — When  nickel  oxide  or  hydrate  is  dissolved 
in  dilute  sulphuric  acid,  and  the  solution  is  allowed  to  evaporate  spontaneously, 
green  crystals  of  tlie  sulphate  with  seven  molecules  of  water  of  crystallization 
are  deposited.      With  ammonium  sulphate,  this  compound  forms  a  double  salt 
in  fine  bluish-green  crystals  containing  NiSO*.(NH4)2S04  +  6H20.     This  is 
the  salt  used  in  nickel-plating. 

537.  TESTS  FOR  NICKEL. — The  anhydrous  nickel  salts  are  yellow,  but  the 
crystallized  salts  and  their  solutions  are  emerald-green.     If  the  solution  be 
acid,  hydrogen  sulphide  produces  no  precipitate,  but  a  black  precipitate  o't' 
sulphide  is  thrown  down  if  the  solution  contain  sodium  acetate.     The  same 
precipitate  is  formed  by  ammonium  sulphide.     The  alkaline   hydrates  and 
carbonates  occasion  pale-green  precipitates.     Ammonia- water  forms  a  green 
precipitate,  which  quickly  dissolves  in  an  excess  of  the  reagent,  yielding  a 
blue  solution. 

538.  MANGANESE,  Mn  =  55. — This  is  an  exceedingly  infu- 
sible metal,  so  hard  that  it  will  scratch  steel.     It  has  been  ob- 
tained by  strongly  heating  a  mixture  of  manganoso-manganic  oxide 
and  sugar.      Three  of  its  oxides  are  found  native  in  the  minerals 
braunite,  Mn203,  pyrolusite,  MnO2,  and  hausmannite,  Mn304. 

539.  MANGANESE  DIOXIDE,  MnO2. — This  compound  is  com- 
monly called  black  oxide  of  manganese.     When  it  is  heated  to 
redness,  it  loses  one-third  of  its  oxygen,  and  is  converted  into  a 
red  powder  of  manganese-manganic  oxide,  Mn304.     This  decom- 
position was  formerly  applied  for  the  preparation  of  oxygen. 

3Mn02        =         Mn304         +         O2 

Oxygen   is  also  evolved,  while  manganous    sulphate  is  formed, 
when  the  dioxide  is  heated  with  sulphuric  acid. 

2Mn02         +         2H2SO*         =         2MnSO*         +         2H20         +         O2 

When  heated  with  hydrochloric  acid,  manganese  dioxide  yields 

manganese  chloride,  water,  and  chlorine :  large  quantities  of  the 

dioxide  are  used  for  the  manufacture  of  chlorine  by  this  reaction, 

and  in  the  solution  of  manganese  chloride  the  dioxide  is  regener- 


MANGANIC    ACID.  323 

ated  by  various  processes.  One  of  these  consists  in  mixing  the 
liquid  with  milk  of  lime,  by  which  calcium  chloride  and  man- 
ganous  hydrate,  Mn(OH)2,  are  formed:  heated  air  is  then  blown 
through  the  mixture,  and  the  manganous  hydrate  is  converted 
into  the  dioxide,  from  which  the  solution  of  calcium  chloride  is 
decanted. 

IN]  unganese  dioxide  is  also  employed  to  decolorize  glass  rendered 
dark  by  carbonaceous  matter  or  green  by  a  trace  of  iron.  In  the 
first  ;ase  it  oxidizes  the  carbon  in  the  glass  pot,  and  in  the  second 
it  nc  itralizes  the  green  color  of  the  ferrous  silicate  by  imparting  a 
redd  sh  tint  of  manganous  silicate. 

5-iO.  MANGANIC  ACID,  H2MnO*. — When  strongly  heated  with 
alkal  ne  hydrates,  manganese  dioxide  absorbs  oxygen  from  the  air, 
and  n  alkaline  manganate  is  formed.  A  mixture  of  manganese 
diox  le  and  potassium  hydrate  may  be  fused  in  a  silver  or  iron 
dish,  and,  when  the  cold  mass  is  treated  with  water,  a  green  solu- 
tion s  obtained.  If  this  be  evaporated  at  a  low  temperature  in  a 
vacu  im,  it  deposits  green  crystals  of  potassium  manganate. 

AY  hen  the  alkaline  manganates  are  heated  to  450°  in  a  current 
of  st  ;am,  they  are  decomposed  into  alkaline  hydrate  and  manga- 
nese iioxide.  This  decomposition  has  been  applied  to  the  manu- 
facture of  oxygen  on  a  large  scale.  A  mixture  of  sodium  hydrate 
and  manganese  dioxide  is  heated  in  a  current  of  air ;  oxygen  is 
absorbed,  and  sodium  manganate  is  formed. 

MnO2         +         2NaOH         +         0  Nu2MnO*         +         H20 

Manga  iese  dioxide.  Sodium  manganate. 

The  air  is  then  stopped,  and  steam  is  passed  over  the  heated 
manganate,  reproducing  sodium  hydrate  and  manganese  dioxide, 
while  oxygen  is  disengaged. 

Na-'MnO*         +         IPO         =         2NaOH         +         MnO2         +         0 

The  oxygen,  with  the  excess  of  steam,  is  led  through  cold 
pipes,  where  the  steam  is  condensed,  while  the  oxygen  passes  on 
to  appropriate  gas-holders. 

541.  PERMANGANATES. — When  the  green  solution  of  potas- 
sium manganate  is  boiled,  its  color  changes  to  red,  while  hydrated 
manganese  dioxide  separates  in  brown  flakes.  The  red  color  is  due 


324  LESSONS    IN   CHEMISTRY. 

to  the  formation  of  potassium  permanganate,  and  the  solution 
contains  free  sodium  hydrate. 

3K2MnO*        +     2H20     =  K2Mn2Q8  +     MnO2     +     4KQH 

Potassium  manganate.  Potassium  permanganate. 

A  similar  reaction  takes  place  when  an  acid  is  added  to  the 
solution  of  a  manganate. 

Potassium  permanganate  is  made  by  heating  in  an  iron  crucible 
a  mixture  of  five  parts  of  potassium  hydrate  with  a  little  water, 
and  three  and  a  half  parts  of  potassium  chlorate  with  four  of 
manganese  dioxide  in  fine  powder.  The  temperature  is  gradually 
raised  to  dull  redness,  the  mass  being  constantly  stirred.  It  is 
allowed  to  cool,  and,  after  being  pulverized,  is  thrown  into  two 
hundred  parts  of  boiling  water,  and  stirred  until  the  liquid  has 
assumed  a  purple  color.  It  is  then  left  to  settle ;  the  clear  liquid 
is  decanted,  neutralized  with  nitric  acid,  and  evaporated  on  a 
water-bath.  The  crystals  which  separate  on  cooling  are  drained 
on  a  clean  brick. 

They  are  purple-black  needles,  having  a  metallic  reflection, 
soluble  in  about  fifteen  times  their  weight  of  cold  water.  The 
solution  has  an  intense  purple  color.  Potassium  permanganate  is 
an  energetic  oxidizing  agent ;  its  solution  is  at  once  decolorized  by 
sulphur  dioxide,  which  it  converts  into  sulphuric  acid,  and  the 
liquid  contains  sulphuric  acid,  potassium  sulphate,  and  manganous 
sulphate. 

K2Mn208     +     5S02     +     2H20     =     K2SO*     +  2MnS04     +     2H2SO* 
Potassium  permanganate.  Manganous  sulphate. 

The  oxidizing  properties  of  potassium  permanganate  are  largely 
employed  in  the  laboratory. 

542.  TESTS  FOR  MANGANESE. — The  salts  of  manganese  are 
colorless  or  pale  rose-colored.  They  are  not  precipitated  by  hydro- 
gen sulphide,  but  ammonium  sulphide  throws  down  flesh-colored 
manganese  sulphide.  The  alkaline  hydrates  produce  dirty-white 
precipitates  of  manganese  hydrate,  which  soon  absorbs  oxygen 
from  the  air  and  becomes  brown.  When  heated  with  a  little 
potassium  hydrate  or  nitrate  or  sodium  carbonate  on  a  piece  of 
platinum  foil,  they  yield  a  greenish  mass  of  an  alkaline  man- 


CHROMIUM.  325 

ganate,  which  forms  a  red  solution  when   treated  with  a  little 
diHte  nitric  acid. 

I  'ranium  is  an  element  closely  related  to  manganese.  One  of  its  principal 
minerals  is  pitchblende,  a  greenish-yellow  oxide.  It  is  used  for  the  prepara- 
tioi  of  sodium  uranate,  which  is  known  as  uranium  yellow ;  this  is  employed 
for  tainting  on  porcelain,  and  for  coloring  a  greenish-yellow  glass  which  is 
hig  ily  fluorescent. 


LESSON    LXI. 
CHROMIUM    AND    TIN. 

•"43.  Chromium,  Cr  =  52.5. — Chromium  exists  in  the  mineral 
ch/'jmite,  which  is  a  compound  of  chromium  oxide  and  ferrous 
oxi  le,  and  may  be  considered  as  ferroso-ferric  oxide  in  which  the 
fer  ic  oxide  is  replaced  by  the  sesquioxide  of  chromium,  FeO.Cr203. 
It  s  found  also  as  lead  chromate  in  the  red  lead  of  Siberia.  The 
me  al  has  been  obtained  by  calcining  a  mixture  of  its  oxide  with 
charcoal  and  oil.  It  then  forms  grayish- white,  metallic  granules, 
wh  ch  are  exceedingly  hard. 

5  4.  CHROMIC  CHLORIDE,  Cr2Cl6,  is  obtained  by  passing  chlorine  gas  over 
an  iacandescent  mixture  of  chromium  sesquioxide  and  charcoal ;  it  then  sub- 
limes and  condenses  in  brilliant  violet  scales  in  the  cooler  parts  of  the  tube. 
By  ihe  action  of  hydrogen  at  a  red  heat,  it  is  converted  into  white  chromous 
chlo  -ide,  CrCl2.  Chromic  chloride  is  insoluble  in  water,  but  dissolves  readily 
in  p  -esence  of  a  small  quantity  of  chromous  chloride,  yielding  a  green  solution 
from  which  there  may  be  obtained  a  crystallized  hydrate,  Cr'2Cl6  +  6H20. 

545.  CHROMIUM  SESQUIOXIDE,  Cr203. — When  potassium  dichromate  is  heated 
in  a  crucible  with  about  half  its  weight  of  sulphur,  a  mass  is  obtained  from 
which  water  dissolves  potassium  sulphate,  leaving  chromium  sesquioxide  as  a 
green  powder.  Instead  of  sulphur,  starch  in  quantity  equal  to  one-fourth 
the  v^eight  of  the  dichromate  may  be  employed,  but  the  resulting  oxide  must 
afterwards  be  recalcined  in  the  air,  to  burn  out  traces  of  carbon.  It  is  in  the 
latte.1'  manner  that  the  fine  chrome  green  used  for  painting  on  porcelain  is  ob- 
tained. Chromium  sesquioxide  is  not  decomposed  by  heat,  and  fuses  only  at 
very  elevated  temperatures.  A  corresponding  hydrate,  Cr2(OH)6,  is  thrown 
down  as  a  bluish-green  precipitate  when  ammonia-water  is  added  to  the 
green  solution  of  chromic  chloride.  The  same  hydrate  is  precipitated  by  the 
alkaline  hydrates,  but  dissolves  in  an  excess  of  the  reagent;  when  the  liquid 
is  boiled,  the  insoluble  oxide  is  thrown  down. 

28 


326  LESSONS    IN    CHEMISTRY. 

546.  CHROMIC  ANHYDRIDE,  CrO3. — This  compound  is  com- 
monly called  chromic  acid.     It  is  prepared  by  mixing  a  cold  satu- 
rated solution  of  potassium  dichromate  with  one  and  a  half  times 
its  volume  of  strong  sulphuric  acid.     As  the  liquid  cools,  chro- 
mium anhydride  separates  in  crimson  needles,  which  are  quickly 
drained  on  a  dry  brick  and  recrystallized  in  the  smallest  possible 
quantity  of  warm  water.     It  is  a  deliquescent  substance,  exceed- 
ingly soluble  in  water,  and  the  solution  has  an  orange  color.     It 
energetically  oxidizes  many  bodies.      With  hydrochloric  acid  it 
forms  water  and  chromium  sesquichloride,  while  chlorine  is  set  free. 

2003     +     12HC1     =     Cr2Cl6     +     6H20     +     3C12 
It  instantly  oxidizes  sulphur  dioxide,  chromium  sulphate  being 
formed. 

2Cr03         +         3S02         =         Cr2(SO*)3 

It  oxidizes  alcohol  and  ether  with  such  energy  that  those  com- 
pounds are  inflamed. 

547.  CHROMATES. — The  solution  of  chromium  anhydride  must 
be  regarded  as  containing  chromic  acid,  H2Cr04  =  H20  -j-  CrO3, 
corresponding  in  molecular  constitution  to  sulphuric  acid.     The 
chromium  compounds  are  all  derived  from  potassium  dichromate, 
which  is  manufactured  from  chrome  iron.     The  pulverized  chro- 
rnite  is  heated  to  redness  with  half  its  weight  of  potassium  nitrate, 
and  the  mass  is  then  exhausted  with  water.     An  impure  solution 
of  potassium  neutral  chromate  is  thus  obtained :  this  is  treated 
with  acetic  acid,  which  combines  with  part  of  the  potassium,  con- 
verting the  neutral  chromate  into  dichromate  ;  the  clear  solution 
of  potassium  dichromate  is  then  decanted  and  evaporated  until  it 
is  ready  to  crystallize. 

548.  Potassium  chromate,  K2Cr04,  forms  beautiful,  lemon -yel- 
low, anhydrous  crystals,  which  are  very  soluble  in  water,  to  which 
they  impart  an  intense  yellow  color. 

549.  Potassium  dichromate,  K2Cr20T,  forms  large,  orange-red 
crystals,  soluble  in  about  eight  times  their  weight  of  cold  water, 
and  in  much  less  boiling  water.     By  heat  they  are  decomposed 
into  potassium  chromate,  chromium  oxide,  and  oxygen. 

2K2O207         =         2K2CrO*         +         Cr203         +         O3 


CHROMIUM.  327 

Potassium  dichromate  is  an  energetic  oxidizing  agent.  When 
heated  with  sulphuric  acid,  it  yields  oxygen,  while  chrome  alum 
wi  1  crystallize  from  the  liquid  obtained  by  treating  the  residue 
with  boiling  water. 

K'WO*     +     4H2SO*     =  =     Cr2(SO*)3.K2SO*     +     4IPO     +     O3 

When  sulphur  dioxide  is  passed  into  a  solution  of  potassium 
di  :hromate,  the  orange  color  is  gradually  replaced  by  green  :  while 
th  3  sulphur  dioxide  becomes  sulphuric  acid,  both  chromium  and 
p<  tassium  are  converted  into  sulphates,  and  the  liquid  will  yield 
cl  rome  alum  if  sulphuric  acid  be  added. 

KWO?     +     3S02     +     H2SO*    =  :     Cr2(S04)3.K2SO*     +     IPO 

.50.  Ammonium  dichromate,  (NH4)2Cr207,  may  be  made  by  dividing  a  solu- 
tit  i  of  chromic  acid  into  two  equal  portions,  neutralizing  one  with  atnmonia- 
\v;  ter,  and  then  adding  the  other.  When  the  solution  is  evaporated,  the  am- 
m>  nium  dichromate  separates  in  red  crystals,  which,  when  heated,  yield  pure 
cL  'omium  trioxide  in  a  curious  pulverulent  form,  resembling  green  tea. 
(NH*)2Cr207  =  Cr2Q3  +  4H20  +  N2 

>51.  Lead  chromate,  PbCrO4,  is  found  native  as  the  red  lead  of  Siberia.  It 
is  made  by  mixing  solutions  of  potassium  chromate  or  dichromate  and  lead 
ac  tate;  potassium  acetate  remains  in  solution,  while  the  lead  chromate  forms 
a  i  ense  yellow  precipitate,  which  when  washed  and  dried  constitutes  chrome 
ye  low.  It  is  insoluble  in  water  and  in  acetic  acid,  but  dissolves  in  solutions 
of  the  alkaline  hydrates.  It  melts  at  a  red  heat,  and  is  readily  reduced  by 
bo  h  hydrogen  and  charcoal.  It  is  sometimes  substituted  for  cupric  oxide  in 
tht  analysis  of  carbon  compounds. 

552.  TESTS  FOR  CHROMIUM. — Although  there  is  a  series  of 
chromous  salts  in  which  the  chromium  atom  is  diatomic,  the 
reactions  of  the  salts  corresponding  to  the  sesquioxide  are  suffi- 
cient to  characterize  this  element.  In  the  green  solutions  of  these 
compounds  hydrogen  sulphide  produces  no  precipitate  :  ammonium 
sulphide  throws  down  chromium  hydrate,  hydrogen  sulphide  being 
disengaged. 

Cr'Cl6     +     3(NH*)2S     +     6H20     =  =     Cr*(OH)«     +     6NH*C1     +     3H2S 

The  alkaline  hydrates  and  ammonia  produce  the  same  green  pre- 
cipitate, which  dissolves  readily  in  an  excess  of  the  former  reagents, 
more  slowly  in  ammonia-water.  When  the  solution  so  obtained 
is  boiled,  anhydrous  chromium  sesquioxide  is  precipitated,  and 
does  not  redissolve  on  cooling. 


328 


LESSONS   IN   CHEMISTRY. 


The  chromates  may  be  identified  by  heating  them  in  a  test- 
tube  with  a  little  common  salt  and  sulphuric  acid.  Irritating  red 
vapors  of  an  oxychloride  of  chromium,  Cr02Cl2,  are  disengaged, 
and  if  conducted  into  a  cold  tube  will  condense  to  a  blood-red 
liquid.  When  passed  into  water,  these  vapors  are  decomposed 
into  hydrochloric  and  chromic  acids,  and  the  liquid  will  yield 
yellow  lead  chromate  when  treated  with  a  solution  of  lead  acetate. 

Cr02Cl2     +     H2Q     =     CrO3     +     2HC1 

553.  Closely  related  to  chromium  in  their  chemical  relations  are  the  elements 
molybdenum  and  tungsten,  the  first  of  which  exists  as  sulphide,  MoS2,  in  the 
mineral  molybdenite,  while  the  second  is  found  in  various  tungstates,  as  in  the 
mineral  wolfram,  which  is  a  tungstate  of  iron  and  manganese.  Both  of  these 
elements  form  trioxides,  which,  like  chromium  trioxide,  are  the  anhydrides  of 
corresponding  acids. 

554.  Tin,  Sn  =  118. — Tin  is  rarely  found  in  the  metallic  state 
in  nature :  its  only  workable  ore  is  the  dioxide,  which  constitutes 
the  mineral  cassiterite.  The  principal  tin-mines  are  in  Wales. 
The  ore  is  crushed,  and  the  dioxide,  being  very  heavy,  can  be 
separated  from  the  lighter  earthy  matters  by  washing  in  a  stream 

of  water.  It  is  then  roasted,  the 
sulphides  and  arsenides  of  iron 
and  copper  present  being  con- 
verted into  oxides,  which  are  re- 
moved by  a  second  washing.  The 
purified  cassiterite  is  mixed  with 
charcoal  and  fed  into  a  cupola 
furnace  (Fig.  125),  where  the 
combustion  is  supported  by  a  blast 
of  air.  The  reduced  tin  collects' 
on  the  hearth  of  the  furnace,  and 
runs  into  a  basin,  where  it  is  stirred 
with  poles  of  green  wood.  The 
gases  given  off  reduce  any  oxide 
FIG.  125.  that  has  been  formed,  and  bring 

to  the  surface  of  the  molten  metal 

the  foreign  matters,  which  form  a  dross.     The  tin  is  then   drawn 
off  into  moulds,  and  is  purified  by  being  melted  at  a  low  temper- 


TIN.  329 

at  are  on  the  inclined  hearth  of  a  reverberatory  furnace.  Being 
in  jre  fusible  than  the  foreign  metals  present,  it  melts  first,  and 
runs  into  a  cavity  prepared  for  it,  while  the  less  fusible  metals 
remain  on  the  hearth. 

Tin  is  a  silvery-white  metal,  having  a  density  of  about  7.3.  It 
milts  at  228°,  and  may  be  crystallized  by  slow  cooling.  It  is 
m  illeable  and  ductile  :  when  a  bar  of  tin  is  bent,  it  produces  a 
piculiar  noise,  called  the  cry  of  tin,  caused  by  the  sliding  of  the 
ci  ystals  over  one  another. 

It  is  not  affected  by  the  air  at  ordinary  temperatures,  but  when 
iu  'Ited  absorbs  oxygen,  and  by  stirring  may  be  entirely  converted 
in  :o  the  dioxide.  It  is  dissolved  by  hydrochloric  acid,  hydrogen 
bi  ing  disengaged,  while  stanuous  chloride  is  formed.  Nitric  acid 
c<  averts  tin  into  dioxide,  giving  off  torrents  of  red  vapors.  Hot 
s<  lutions  of  the  alkaline  hydrates  dissolve  tin,  forming  alkaline 
st  innates,  and  disengaging  hydrogen. 

Tin  is  used  for  the  manufacture  of  tin  foil,  employed  for 
ei  veloping  tobacco,  chocolate,  etc. ;  also  for  tinning  copper  and 
ir  )n,  which  is  accomplished  by  dipping  the  perfectly  clean  objects 
into  a  bath  of  molten  tin.  Its  resistance  to  the  action  of  vegetable 
acids  renders  it  invaluable  as  a  coating  for  culinary  utensils.  It 
ei  ters  into  the  composition  of  plumbers'  solder,  which  is  an  alloy 
oi  tin  and  lead.  Bronze,  bell-metal,  gun-metal,  and  speculum- 
matal  are  alloys  of  tin  and  copper  (page  287).  Britannia  metal 
is  tin  alloyed  with  a  small  proportion  of  antimony,  bismuth,  and 
copper. 

In  its  compounds  tin  is  either  diatomic  or  tetratomic.  Those 
in  which  it  is  diatomic  are  called  stannous  compounds,  while  in 
the  stannic  compounds  it  is  tetratomic,  one  atom  of  tin  having  the 
same  combining  power  as  four  atoms  of  hydrogen. 

555.  STANNOUS  CHLORIDE,  SnCl2. — Anhydrous  stannous  chlo- 
ride is  obtained  by  passing  hydrochloric  acid  gas  over  heated  tin. 
It  is  a  white  solid,  fusible  at  250°.  When  it  is  dissolved  in  a 
small  quantity  of  water,  or  when  metallic  tin  is  dissolved  in  hot 
hydrochloric  acid,  a  solution  is  obtained  which  when  sufficiently 
concentrated  deposits  crystals  of  a  hydrate  containing  SnCl2  -j- 

28* 


330  LESSONS    IN    CHEMISTRY 

2 IPO.  These  crystals  are  known  in  commerce  as  tin  salt  or  tin 
crystals.  They  are  soluble  in  a  small  quantity  of  water,  but  when 
the  solution  is  diluted,  a  deposit  of  an  oxychloride  is  formed  con- 
taining SuCP.SnO.  At  the  same  time  a  certain  proportion  of 
the  stannous  chloride  is  converted  into  stannic  chloride,  SnCl4. 
This  decomposition  is  prevented  by  the  presence  of  free  hydro- 
chloric acid,  or  by  a  small  quantity  of  ammonium  chloride.  Stan- 
nous  chloride  is  a  reducing  agent :  a  few  drops  of  its  solution 
instantly  decolorize  the  purple  solution  of  potassium  permanga- 
nate ;  it  reduces  the  salts  of  silver  and  gold,  setting  free  the  metal. 
When  it  is  added  to  a  solution  of  mercuric  chloride,  a  white  pre- 
cipitate of  mercurous  chloride  is  formed,  which  an  excess  of 
stannous  chloride  converts  into  a  gray  deposit  of  finely-divided 
metallic  mercury.  In  these  reactions  the  stannous  chloride  be- 
comes stannic  chloride.  Stannous  chloride  is  used  as  a  mordant 
in  dyeing. 

556.  STANNIC  CHLORIDE,  SnCl4,  is  formed  with  the  production  of  light  and 
heat  by  the  direct  union  of  tin  and  chlorine.     It  is  prepared  by  passing  dry 
chlorine  over  melted  tin  contained  in  a  retort;  it  then  distils,  .and  condenses 
as  a  heavy,  fuming,  yellow  liquid,  which  boils  at  120°.     It  combines  energeti- 
cally with  water,  forming  crystals  of  a  hydrate  containing  SnCl*  +  5H20.    The 
same  hydrate  may  be  made  by  dissolving  tin  in  hydrochloric  acid  and  from 
time  to  time  adding  small  quantities  of  nitric  acid.     The  crystals  are  soluble 
in  water,  yielding  a  limpid  solution. 

557.  STANNIC  OXIDE,  SnO2. — When  an  alkaline  hydrate  is  added  to  a  solu- 
tion of  stannous  chloride,  stannous  hydrate  is  formed  as  a  white  precipitate, 
which,  by  boiling,  is  converted  into  black  stannous  oxide,  SnO.     The  addition 
of  ammonia  to  a  solution  of  stannic  chloride  throws  down  a  white  gelati- 
nous precipitate  of  stannic  hydrate,  H2Sn03,  which  by  the   action  of  heat  is 
converted  into  stannic  oxide,  SnO2.     This  compound  is  found  in  nature  in 
hard,  transparent  crystals;  it  is  cassiterite.     It  is  an  acid  oxide,  and  stannic 
hydrate  reacts  with   the  bases,  forming  stannates  whose  compositions  corre- 
spond to  the  carbonates.     The  white  powder  produced  by  the  action  of  nitric 
acid  on  tin  is  a  stannic  hydrate,  containing  Sn(OH)4  =  SnO2  +  2H20. 

558.  Sulphides  of  Tin. — By  heating  together  the  proper  proportions  of  tin 
and  sulphur,  two  sulphides  may  be  obtained.     Stannous  sulphide,  SnS,  is  a 
gray,  crystalline  mass.     The  preparation  of  stannic  sulphide,  SnS2,  requires 
particular  precautions  ;  an  amalgam  of  tin  with  half  its  weight  of  mercury 
is  mixed  with  flowers  of  sulphur  and  ammonium  chloride  and  heated  to  dull 
redness.     Mercuric  sulphide,  ammonium  chloride,  and  the  excess  of  sulphur 
sublime,  while  the  interior  of  the  vessel  becomes  lined  with  a  golden-yellow, 


PLATINUM    AND    ITS    ALLIED    METALS.  331 

crystalline  mass  of  stannic  sulphide.  The  operation  must  then  be  arrested, 
or  1  his  compound  will  be  decomposed  into  stannous  sulphide  and  sulphur;  the 
addition  of  the  mercury  and  ammonium  chloride  is  intended  to  keep  the  tem- 
perature down  to  the  volatilizing  points  of  mercuric  sulphide  and  ammonium 
chl<  ride.  Stannic  sulphide  forms  soft,  crystalline  scales,  called  mosaic  gold. 

f'59.  TESTS  FOR  TIN. — In  stannous  solutions,  both  hydrogen 
sul )hide  and  ammonium  sulphide  form  brown  precipitates,  soluble 
in  in  excess  of  ammonium  sulphide.  The  alkaline  hydrates  and 
am  nonia  give  white  precipitates,  soluble  in  an  excess  of  the  former 
rea  ;ents,  but  insoluble  in  ammonia.  '  Gold  trichloride  throws  down 
pui  pie  of  Cassius.  In  mercuric  chloride  solutions,  an  excess  of 
stai  nous  chloride  precipitates  gray  metallic  mercury. 

1  n  stannic  solutions,  hydrogen  sulphide  and  ammonium  sulphide 
form  yellow  precipitates,  soluble  in  a  large  quantity  of  the  latter 
rea  ;ent.  Apiece  of  zinc  placed  in  either  a  stannous  or  a  stannic 
soh  tion  becomes  covered  with  a  deposit  of  tin,  which  may  be 
ren  lered  brilliant  by  burnishing. 

5(  0.  The  elements  titanium,  zirconium,  and  thorium  closely  resemble  tin  in 
thei  chemical  relations,  although  their  physical  properties  are  very  differ- 
ent. Each  forms  a  tetrachloride  and  a  dioxide.  Titanium  is  found  native 
as  (1  oxide  in  the  minerals  rutile,  anatase,  and  brookite.  Zirconium  occurs 
as  a  silicate  in  the  mineral  zircon. 


LESSON    LXIL 
PLATINUM  AND   ITS  ALLIED   METALS. 

5(51.  Like  gold,  platinum  is  found  in  the  metallic  state  in 
rounded  granules  distributed  through  sandy  deposits.  Being 
very  heavy,  it  is  also  separated  like  gold,  by  washing  the  sand  in 
a  stream  of  water.  The  native  platinum,  however,  is  not  pure  : 
besides  containing  traces  of  gold,  copper,  and  iron,  it  is  alloyed 
with  several  other  metals  which  it  resembles  in  certain  properties, 
and  which  are  called  the  platinum  metals.  They  are  rhodium, 
ruthenium,  palladium,  indium,  and  osmium.  The  platinum  is 
extracted  by  treating  the  grains  first  with  dilute  nitre-hydrochloric 


332  LESSONS    IN    CHEMISTRY. 

acid,  which  removes  all  excepting  the  platinum  metals,  and  then 
heating  it  with  strong  nitre-hydrochloric  acid,  which  dissolves  the 
platinum,  leaving  osmium  and  the  greater  part  of  the  iridium. 
The  liquid  is  then  exactly  neutralized  with  sodium  carbonate,  and 
a  solution  of  mercuric  cyanide  is  added.  This  throws  down  a 
precipitate  of  palladium  cyanide,  which  is  removed  by  filtration, 
and  the  clear  liquid  is  treated  with  ammonium  chloride.  A  crys- 
talline precipitate  of  a  double  chloride  of  platinum  and  am- 
monium forms,  and  this,  when  calcined,  leaves  a  porous  gray 
residue  of  platinum  sponge.  Platinum  so  prepared  always  con- 
tains some  iridium,  for  the  latter  metal  also  separates  as  a  double 
chloride  when  the  ammonium  chloride  is  added. 

In  order  to  agglomerate  the  spongy  platinum,  it  is  made  into 
a  stiff  paste  with  a  little  water,  and  this  is  strongly  compressed 
in  a  slightly  conical  steel  cylinder.  It  is  then  removed,  heated  to 
whiteness,  and  converted  into  a  solid  mass  by  hammering.  Plati- 
num is  also  melted  in  lime  crucibles,  heated  by  the  flame  of  the 
oxyhydrogen  blow-pipe  directed  against  the  mass  of  metal. 

Platinum  is  a  white  metal,  having  a  somewhat  gray  lustre. 
Its  density  is  21.5.  It  is  very  malleable  and  ductile.  It  melts 
only  at  the  highest  attainable  temperatures,  but  at  a  white  heat 
it  becomes  soft  and  can  be  forged  and  welded  like  iron.  It  is 
not  affected  j?y  the  air  at  any  temperature,  and  does  not  dissolve 
in  either  hydrochloric,  sulphuric,  or  nitric  acid.  When  it  is 
alloyed  with  silver,  it  is  dissolved  by  nitric  acid.  Nitro-hydro- 
chloric  acid  dissolves  it  slowly  in  the  cold,  more  rapidly  by  the  aid 
of  heat,  converting  it  into  the  tetrachloride.  The  alkaline  hydrates 
and  nitrates  attack  it  at  a  high  temperature,  and  these  substances 
must  not  be  fused  in  platinum  crucibles. 

Platinum  has  the  power  of  condensing  gases  in  its  pores,  and 
we  have  already  seen  how  the  oxidation  of  ammonia  and  vapor 
of  alcohol  and  ether  may  be  effected  by  a  platinum  wire.  This 
property  is  more  strongly  manifested  by  platinum  sponge  than 
by  the  compact  metal,  and  hydrogen  escaping  from  a  jet  may 
be  ignited  by  holding  in  it  a  morsel  of  recently-heated  spongy 
platinum.  When  a  solution  of  platinic  chloride  is  boiled  with 


PLATINUM   AND    ITS   ALLIED    METALS.  333 

potassium  hydrate,  and  alcohol  is  added  to  the  boiling  liquid 
with  constant  stirring,  metallic  platinum  is  deposited  as  a  black 
powder.  This  powder,  which  is  called  platinum  black,  is  in  a 
stat<3  of  extreme  division,  and  brings  about  the  oxidation  of  corn- 
bus  ible  gases  and  vapors  even  more  readily  than  platinum  sponge. 

I'latinum  is  employed  for  the  manufacture  of  crucibles  and 
disles  for  the  laboratory,  for  it  not  only  resists  high  temperatures 
but  is  attacked  by  very  few  chemical  reagents.  It  is  manufac- 
tur<  d  into  large  retorts  for  the  concentration  of  sulphuric  acid. 
All  of  this  apparatus  is  made  as  thin  as  is  consistent  with  strength, 
for  he  metal  is  costly. 

1'latiuum  forms  two  series  of  compounds, — platinous  compounds, 
in  ^hich  it  is  diatomic,  and  platinic  compounds,  in  which  it  is 
tetr  itomic. 

5  _>2.  PLATINIC  CHLORIDE,  PtCl4,  is  made  by  dissolving  the 
met  il  in  nitro-hydrochloric  acid.  When  the  reddish-brown  liquid 
is  si  fficiently  concentrated,  it  deposits,  on  cooling,  hydrated  crys- 
tals of  platinic  chloride,  which  may  be  rendered  anhydrous  by 
heal .  The  anhydrous  salt  is  a  red-brown  deliquescent  mass,  very 
soluble  in  water,  alcohol,  and  ether.  When  its  solution  is  added 
to  s<  lution  of  potassium  chloride  or  ammonium  chloride,  a  yellow 
crys  alline  precipitate  of  a  double  chloride  of  platinum  with  potas- 
siun  or  ammonium  is  formed.  These  salts  are  not  very  soluble 
in  c  )ld  water,  and  are  still  less  soluble  in  alcohol,  the  potassium 
compound  being  more  soluble  than  that  of  ammonium.  Their 
compositions  are  PtCl4.2KCl  and  PtCl4.2NH4Cl.  When  the 
ammonium  salt  is  heated,  it  leaves  a  residue  of  spcragy  platinum. 

If  platinum  tetrachloride  be  carefully  heated  to  200°,  chlorine 
is  disengaged;  and  if  the  residue  be  extracted  with  boiling  water, 
the  unaltered  platinic  chloride  is  dissolved,  while  platinum  dichlo- 
ride,  PtCl2,  remains  as  an  olive-green  powder. 

Of  the  other  metals  of  the  platinum  group,  OSMIUM  is  the  least  fusible :  it 
has  never  been  melted.  When  strongly  heated  in  the  air,  it  forms  a  volatile 
oxide,  which  is  one  of  the  most  dangerous  poisons  known.  It  is  the  heaviest 
known  element,  having  a  density  of  22.48. 

563.  PALLADIUM  is  the  most  fusible  of  these  metals,  :md  has  the  lowest 
density,  its  specific  weight  being  11.4.  When  a  piece  of  tliis  metal  is  made 


334  LESSONS    IN    CHEMISTRY. 

the  negative  electrode  of  an  apparatus  in  which  water  is  being  decomposed 
by  the  voltaic  current,  it  will  absorb  about  nine  hundred  times  its  volume  of 
hydrogen. 

564.  IRIDIUM  often  constitutes  a  considerable  proportion  of  platinum  ore, 
which  is  then  called  platiniridium  or  osmiridium,  as  platinum  or  osmium  pre- 
ponderates in  the  alloy.     Iridium  alloyed  with  90  per  cent,  of  platinum  is  as 
hard  and  elastic  as  steel,  is  less  fusible  than  platinum,  and  is  unaltered  by  the 
air.     It  is  used  for  the  points  of  gold  pens  and  ink-containing  pencils,  as  is 
also  the  native  alloy,  osmiridium.     The  density  of  iridium  is  22.38. 

565.  RHODIUM  is  more  fusible  than  iridium,  but  less  fusible  than  platinum. 
Its  density  is  12.1.     It  does  not  dissolve  in  nitro-hydrochloric  acid  unless  it  is 
alloyed  with  other  metals. 

566.  RUTHENIUM  is  the  most  infusible  metal  after  osmium.     Its  density  is 
12.26.     It  is  hardly  attacked  by  boiling  nitro-hydrochloric  acid. 


LESSON    LXIII. 
THE  CHEMISTRY   OP  LIFE. 

567.  Under  the  influence  of  the  mysterious  principle  which 
we  call  life,  certain  chemical  compounds  undergo  a  complete  meta- 
morphosis. Their  elements  become  rearranged  in  manners  which 
are  beyond  our  methods  of  research,  and  the  matter  becomes  or- 
ganized.  It  assumes  certain  definite  forms  which  we  call  cells, 
and  living  cells  are  gifted  with  a  wonderful  power  of  reproduc- 
tion :  under  the  proper  conditions  they  can  convert  unorganized 
dead  matter  into  other  cells,  either  of  the  same  kind  or  of  very 
different  kinds  related  by  progressive  modifications.  Chemists 
are  able  to  change  one  form  of  matter  into  another, — to  modify 
and  destroy  molecules,  and  to  construct  new  molecules ;  they  are 
unable  to  create  the  simplest  cell,  the  lowest  form  of  organized 
matter.  We  have  no  reason  to  believe  that  any  cell  is  ever  pro- 
duced except  from  another,  but  we  know  that  under  modified  cir- 
cumstances the  nature  of  the  cell  may  in  the  course  of  succes- 
sive reproductions  become  completely  modified,  and  new  forms  of 
organized  matter  are  produced. 

The  elements  which  enter  into  the  composition  of  organized 


THE   CHEMISTRY   OF   LIFE.  335 

matter  are  comparatively  few:  all  vital  tissues  contain  carbon, 
hydrogen,  and  oxygen,  and  these  three,  together  with  nitrogen 
and  a  few  salts,  principally  phosphates,  chlorides,  and  sulphates  of 
sodi  im,  potassium,  and  calcium,  constitute  the  greater  part  of  all 
tissues,  vegetable  and  animal.  Plants  and  vegetables  directly  con- 
vert carbon  dioxide  and  water  into  cellulose,  starch,  hydrates  of 
carb  )n,  and  other  compounds,  among  which  are  even  hydrocar- 
bon.-. In  this  reducing  action  of  vegetable  life  on  carbon  dioxide 
and  tfater,  the  atoms  of  carbon  and  hydrogen  recover  part  of  the 
energy  which  disappears  from  them  in  the  formation  of  those 
compounds.  As  far  as  their  matter  is  concerned,  plants  then  act 
as  s  orers  or  regenerators  of  energy.  In  the  natural  heat  and 
mot!  3n  of  animals  the  atomic  energy  of  the  compounds  of  carbon 
and  hydrogen  is  manifested  as  those  compounds  are  again  oxidized 
with  the  formation  of  carbon  dioxide  and  water.  Animal  life  is 
real!  y  dependent  on  the  continual  expenditure  of  energy.  Vege- 
tabli  s  can  receive  their  nutrition  directly  from  mineral  matter, 
but  inimals  can  form  tissues  only  from  matter  that  has  first  been 
prep  ired  by  vegetables  or  other  animals. 

However,  besides  the  carbon,  hydrogen,  and  oxygen,  plants 
absorb  nitrogen  from  nitrogenized  matters  in  the  soil,  and  the 
nitrogen  compounds  of  plants  are  essential  for  the  nutrition  of 
animals.  We  must  study  some  of  the  compounds  which  have 
thus  far  been  formed  only  under  the  influence  of  life,  and  of 
which  the  organization  results  in  the  production  of  cells.  Among 
these  substances,  which  we  must  remember  are  not  chemical  com- 
pounds of  definite  and  known  constitution,  of  first  importance  are 
the  albuminoid  matters. 

ALBUMINOID   AND   GELATINOID   SUBSTANCES. 

5G8.  These  complex  matters  are  composed  of  carbon,  hydrogen, 
oxygen,  and  nitrogen,  and  often  a  small  proportion  of  sulphur. 
By  their  compositions  and  properties,  they  are  all  related  to  the 
albumen  of  white  of  egg,  or  to  the  gelatin  or  glue  which  can  be 
extracted  from  bones.  If  flour  made  from  wheat  or  other  cereal 
be  kneaded  in  water,  the  starch  is  washed  out,  while  a  gray  elastic 


336  LESSONS   IN   CHEMISTRY. 

mass  of  gluten  remains.  This  gluten  may  be  separated  into  sev- 
eral different  substances,  having  different  degrees  of  solubility  in 
alcohol :  they  are  of  similar  composition,  containing  a  little  more 
than  50  per  cent,  of  carbon,  7  of  hydrogen,  17  of  nitrogen,  20  of 
oxygen,  and  rather  less  than  one  per  cent,  of  sulphur.  The  water 
used  in  the  preparation  of  gluten  contains  another  matter,  which 
may  be  separated  by  allowing  the  starch  to  settle,  adding  a  few 
drops  of  acid  to  the  clear  liquid,  and  heating  to  the  boiling  point. 
An  albuminoid  matter  then  coagulates  in  white  flakes.  Its  com- 
position does  not  differ  greatly  from  that  of  the  bodies  separated 
from  gluten,  but  there  are  slight  differences  depending  on  the 
grain  or  seed  from  which  the  substance  is  derived.  From  the 
seeds  of  leguminous  vegetables,  such  as  peas,  beans,  and  lentils,  a 
body  called  legumine  may  be  extracted,  and,  in  addition  to  the  ele- 
ments contained  in  gluten  and  other  vegetable  albumens,  this  sub- 
stance contains  a  small  percentage  of  phosphoric  acid,  probably  in 
the  form  of  a  substituted  acid,  in  which  various  carbon  groups 
replace  one  or  more  hydroxyl  groups  of  orthophosphoric  acid. 

The  albuminoid  matters  of  animals,  which  are  derived  from  the 
similar  vegetable  substances,  are  classified  more  with  reference  to 
their  behavior  under  the  action  of  heat  than  according  to  their 
composition,  which  varies  but  little.  They  may,  however,  be 
arranged  in  two  groups, — albuminoid  matters  and  gelatin -like 
compounds. 

The  general  composition  of  these  bodies  is  as  follows : 

Albumen  Group.  Gelatin  Group. 

Carbon 53.5  50.0 

Hydrogen 6.9  6.6 

Oxygen     . 23.0  26.1  to  23.1 

Nitrogen 15.6  16.8 

Sulphur    .........       1.0  0.5  to  3.5 

Of  the  albuminoid  matters  we  can  consider  only  albumen, 
fibrin,  casein,  and  hemoglobin. 

569.  ALBUMEN  exists  in  a  soluble  form  and  an  insoluble  modi- 
fication. Soluble,  it  occurs  in  white  of  egg,  and  in  the  serum  or 
clear  liquid  of  blood ;  but  even  these  forms  present  certain  differ- 
ences. If  either  of  these  liquids  be  evaporated  at  a  low  temper- 


ALBUMINOID    BODIES.  337 

ature,  the  albumen  remains  as  a  transparent,  yellowish,  gum- 
like  mass,  which  is  perfectly  soluble  in  water.  It  is  not  pure,  but 
contains  a  small  quantity  of  alkaline  carbonate  and  certain  salts. 
If  i-  solution  of  albumen  be  heated  to  70°,  it  becomes  clouded, 
and  at  a  few  degrees  higher  the  albumen  separates  either  in  flakes 
or  i  i  a  solid  mass,  according  to  the  concentration  of  the  solution. 
Th<  soluble  albumen  has  coagulated  and  has  become  insoluble 
albi  men.  Solutions  of  albumen  are  also  coagulated  by  the  addi- 
tion of  either  sulphuric,  nitric,  or  hydrochloric  acid,  or  of  certain 
salt  ,  such  as  mercuric  chloride  and  lead  acetate.  Metaphosphoric 
acid  instantly  precipitates  albumen  from  its  solutions.  Ortho- 
pho  ;phoric  acid,  acetic  and  lactic  acids,  form  no  precipitates  with 
albi  men,  neither  does  common  salt  unless  acetic  acid  be  present. 

5  TO.  FIBRIN. — When  fresh  blood  is  allowed  to  stand,  it  soon 
sep;  rates  into  a  yellow  liquid,  called  serum,  and  a  red  coagulum  or 
clot  The  clot  contains  the  red  corpuscles,  the  oxygen-carriers  of 
the  blood,  imprisoned  in  a  mass  of  insoluble  albuminoid  matter. 
By  beating  the  fresh  blood  with  a  bunch  of  twigs  or  an  egg- 
beat  3r,  the  mass  of  blood  is  prevented  from  coagulating,  and  the 
albuminoid  matter,  which  is  called  fibrin,  becomes  attached  to  the 
beat  3r  in  red  flakes.  By  washing  in  a  stream  of  water,  the  red 
corpuscles  are  washed  'out,  and  the  fibrin  remains  as  light-gray, 
elastic  filaments.  It  is  insoluble  in  water,  but  dissolves  in  very 
dilute  alkaline  solutions.  Fibrin  is  formed  by  the  union  of  two 
substances  contained  in  the  blood,  whenever  that  liquid  is  kept  at 
rest.  Its  spontaneous  coagulation  causes  the  cessation  of  bleeding 
from  slight  cuts  and  other  small  wounds. 

The  stiffening  of  the  muscles  which  takes  place  soon  after  death, 
is  due  to  the  coagulation  of  a  peculiar  albuminoid  matter,  called 
myo.-iin,  which  exists  in  solution  in  the  muscular  tissues.  It  is 
soluble  in  water  containing  10  per  cent,  of  salt,  but  is  precipitated 
by  a  larger  quantity  :  it  is  extracted  by  virtue  of  this  property. 

571.  HEMOGLOBIN    is  a  crystallizable  matter  which  can  be 

extracted  from  the  red  corpuscles  of  blood.     It  contains  a  small 

proportion  of  iron.     Hemoglobin  has  the  property  of  absorbing 

oxygen  and  forming  an  unstable  compound  from  which  the  oxygen 

p        w  29 


338  LESSONS    IN    CHEMISTRY. 

escapes  by  exposure  in  a  vacuum.  It  is  probably  by  this  property 
of  the  hemoglobin  which  they  contain,  that  the  red  blood  cor- 
puscles are  enabled  to  carry  oxygen  to  all  parts  of  the  system. 
Hemoglobin  will  also  absorb  carbon  monoxide,  and  when  it  has 
absorbed  that  gas  it  is  incapable  of  combining  with  oxygen  :  this 
explains  the  poisonous  effects  of  carbon  monoxide  on  the  system. 
Hydrogen  sulphide  reduces  hemoglobin, — that  is,  removes  its 
oxygen ;  and  we  can  so  understand  the  injurious  action  of  any 
quantities  of  this  gas. 

572.  CASEIN,  MILK. — Milk  is  a  dilute  solution  of  lactose  or 
milk  sugar  and  a  small  quantity  of  mineral  salts,  in  which  are 
suspended  very  small  fat  globules,  and,  either  suspended  or  in 
solution,  an  albuminoid  matter  called  casein.  The  specific  gravity 
of  milk  is  about  1030.  After  standing  for  several  hours,  the 
greater  number  of  the  fat  globules  come  to  the  surface,  consti- 
tuting the  cream ;  cream,  however,  contains  some  lactose,  casein, 
and  salts.  Its  composition  varies  greatly,  as  may  be  seen  from  the 
following  results  of  the  analysis  of  three  samples : 

i.  ii.  in. 

Water 72.2  66.36  50 

Fat 19.0  18.87  43.9 

Casein,  lactose,  salts 8.8  14.77  6.1 

The  following  is  the  composition  of  an  average  sample  of  cow's 
milk,  but  it  must  be  borne  in  mind  that  no  two  samples  will  prob- 
ably have  the  same  composition.  In  one  thousand  parts,  this  milk 
contained  128  parts  of  solid  matter,  constituted  as  follows: 

Casein 35.70 

Butter 33.80 

Lactose  and  salts 58.50 

When  an  acid  is  added  to  milk,  a  thick  deposit  of  coagulated 
casein  is  formed.  This  same  substance  is  formed  when  milk  nat- 
urally becomes  sour  by  the  formation  of  lactic  and  acetic  acids. 
During  the  first  stages  of  the  souring  of  milk,  lactic  acid  is  pro- 
duced by  the  fermentation  of  the  lactose,  but,  unless  a  large  quan- 
tity of  lactic  acid  be  present,  this  alone  will  not  coagulate  the 
casein  ;  as  soon,  however,  as  acetic  acid  begins  to  form,  the  casein 


THE   CHEMISTRY   OF   LIFE.  339 

becomes  insoluble  and  the  milk  thickens.  Casein  closely  re- 
sembles insoluble  albumen;  it  dissolves  in  dilute  solutions  of  the 
alkaline  hydrates  and  carbonates,  and  it  is  probably  in  solution  in 
fre.sii  milk,  for  that  liquid  has  an  alkaline  reaction.  Cheese  is 
modified  casein. 

573.  GELATIN. — When  bones  are  immersed  in  hydrochloric 
acu  ,  the  mineral  matter,  consisting  principally  of  calcium  phos- 
pha  e  and  carbonate,  is  dissolved,  and  a  semi-transparent,  elastic 
ma.-  s  is  obtained,  retaining  the  form  t)f  the  bone.     This  body  is 
insc  luble  in  cold  water,  but  by  long  boiling  it  dissolves,  and,  on 
cooiing,  the  solution  sets  in  a  transparent  jelly.     This  substance 
is  g  ilatin,  or  glue.     It  is  not  peculiar  to  the  bones,  but  exists  also 
in  c  jrtain  other  tissues,  particularly  in  the  skin,  and  in  the  swim- 
mi  ij  ^-bladders  of  fishes.     The  best  gelatin  is  obtained  from  the 
swi)  iming-bladder  of  the  sturgeon;  it  is  called  fish-glue.     Very 
littl )  is  known  regarding  the  difference  between  gelatin  and  the 
sub  tances  from  which  it  is  derived. 

I  ry  gelatin  occurs  in  transparent  or  translucid  sonorous  sheets, 
whc  se  color  varies  from  colorless  to  brown,  according  to  the  purity. 
It  s  veils  in  water,  but  does  not  dissolve  until  the  liquid  is  heated. 
Its  solution  is  precipitated  by  alcohol,  but  not  by  acids,  with  the 
exception  of  tannic  acid,  with  which  it  forms  an  insoluble  com- 
pound. The  tanning  of  skins  and  hides  depends  on  the  formation 
of  this  compound  in  the  body  of  the  skin,  which  is  so  converted 
into  leather. 

574.  By  the  processes  of  digestion,  the  vegetable  and  animal 
matters  which  serve  as  food  are  converted  into  substances  which 
can  be  assimilated  or  made  part  of  our  bodies.     These  processes 
begin  in  the  mouth,  where  the  starchy  substances  encounter  in 
the  saliva  a  peculiar  unorganized  ferment  called  ptyalin,  which  is 
capable  of  transforming  them  into  soluble  glucose.     Ptyalin  is 
probably  identical  with  diastase,  which  is  formed  during  the  germi- 
nation of  grain.     In  the  stomach,  the  conversion  of  starch  into 
glucose  continues,  and  the  albuminoid  matters  are  converted  into 
soluble  bodies  called  peptones  by  another  ferment, pepsin,  contained, 


340  LESSONS    IN   CHEMISTRY. 

together  with  a  little  hydrochloric  acid,  in  the  gastric  juice.  This 
ferment  exists  in  rennet,  obtained  from  the  stomach  of  the  calf, 
and  used  in  the  manufacture  of  cheese.  The  peptones  appear  to 
be  formed  by  the  hydration  of  the  albuminoid  bodies,  and  in 
the  system  they  are  probably  converted  into  all  the  varieties  of 
albuminoid  tissue.  As  the  food  passes-  from  the  stomach  it 
encounters  in  the  small  intestines  other  ferments,  by  which  the 
fatty  matters  are  emulsified  and  rendered  capable  of  being  ab- 
sorbed and  passing  into  the  blood,  by  which  they  are  carried 
and  deposited  where  needed  in  the  system. 

The  slow  combustion  by  which  life  is  sustained  results  in  the 
oxidation  of  the  tissues,  and  the  removal  of  the  matters  no  longer 
useful.  This  oxidation  is  not  accomplished  in  one  operation,  but 
in  several  stages,  during  which  many  compounds  intermediate 
between  the  albuminoid  and  fatty  bodies,  and  the  carbon  dioxide, 
water,  and  nitrogen  which  would  result  from  their  complete  com- 
bustion, are  formed.  We  have  seen  that  a  great  part  of  the  carbon 
and  hydrogen  is  indeed  removed  as  carbon  dioxide  and  water,  but 
the  salts  are  in  great  part  eliminated  unchanged  by  the  urine  and 
the  perspiration.  The  nitrogen  is  excreted  principally  as  urea, 
phosphorus  as  sodium  acid  phosphate,  sulphur  as  sodium  sulphate, 
etc.  A  small  part  of  the  nitrogen  of  the  system  is  excreted  in 
forms  intermediate  between  the  albuminoid  bodies  and  urea. 
Among  the  more  important  of  these  is  uric  acid,  C5H4N403,  a 
compound  forming  a  small  proportion  of  human  urine,  and  exist- 
ing in  large  quantity  in  the  solid  urine  of  birds  and  reptiles. 

In  all  these  processes  there  is  comparatively  little  that  we  can 
understand.  We  know  only  that  they  all  result  in  a  transfer  of 
energy, — that  in  living  matter  the  chemical  energy  is  converted 
into  the  energy  of  life  ;  and  we  can  comprehend  only  the  beginning 
and  the  end  of  the  phenomenon, — the  forms  of  matter  which  are 
capable  of  organization,  and  the  products  of  the  disorganization 
without  which  life  could  not  continue. 


APPENDIX. 


CRYSTALLOGRAPHY. 

V  crystal  is  a  natural  polyhedron  ;  that  is,  a  solid  bounded  by  plane 
su  faces  or  faces.  The  greater  number  of  solid  chemical  substances 
fu:  in  more  or  less  perfect  crystals  whenever  a  certain  freedom  of  mo- 
tit  11  is  communicated  to  their  molecules,  so  that  these  molecules  may 
ar  ange  themselves  without  interference.  Such  freedom  of  motion 
ni;  y  be  given  to  the  molecules  : 

.  By  dissolving  the  solid  in  any  liquid  by  which  it  is  not  altered, 
an  I  allowing  a  hot  saturated  solution  to  cool  slowly,  or  by  the  spon- 
tai  eous  evaporation  of  the  solvent  if  the  solid  be  equally  soluble  at 
all  temperatures.  Potassium  chlorate,  lead  iodide,  potassium  nitrate, 
an' I  alum  may  be  crystallized  from  water  by  the  first  method;  com- 
m<  n  salt  by  the  second. 

1.  By  melting  the  solid,  and  decanting  the  still  liquid  portion  after 
a  crust  has  formed  on  its  surface.  Sulphur  and  bismuth  may  be  so 
crystallized. 

8.  By  subliming  the  solid,  and  allowing  the  vapor  to  condense 
very  slowly.  In  this  manner  fine  crystals  of  iodine  and  camphor 
may  be  obtained. 

4.  By  a  chemical  reaction  in  which  the  crystallizable  substance  is 
formed  in  a  medium  in  which  it  is  insoluble.  Platino-potassium  chlo- 
ride and  potassium  acid  tartrate  are  so  formed  in  microscopic  crystals. 

A  solid  which  manifests  no  tendency  to  become  crystalline  is  said 
to  be  amorphous. 

For  convenience'  sake,  crystals  are  classified  in  six  systems,  and 
each  system  is  characterized  by  a  set  of  axes,  which  are  imaginary 
straight  lines  passing  through  the  centre  of  the  crystal  and  joining 
opposite  solid  angles  or  the  centres  of  opposite  faces  or  edges.  The 
forms  belonging  to  any  one  system  may  be  derived  from  each  other 

29*  341 


342 


APPENDIX. 


by  cutting  off  the  edges  or  angles  by  plane  surfaces ;  in  all  such  de- 
rivatives the  imaginary  axes  must  remain  untouched. 

1.  THE  ISOMETRIC  SYSTEM  has  three  equal  axes  at  right  angles  to 
each  other.  The  type  of  the  system  is  the  cube  (a),  in  which  the  axes 
join  the  centres  of  opposite  faces.  The  regular  tetrahedron  (6)  is  de- 
rived from  the  cube  by  cutting  off  every  other  solid  angle  by  a  plane 
which  passes  through  the  three  adjacent  angles.  The  regular  octa- 
hedron (c)  is  formed  by  cutting  off  in  the  same  manner  all  the  solid 
angles.  The  rhombic  dodecahedron  (d)  results  when  all  the  edges  are 
cut  off  by  planes  which  meet  in  the  centres  of  the  faces. 


I    ! 


J...-4 


(a) 


2.  THE  QUADRATIC  SYSTEM  has  three  axes  at  right  angles  to  each 
other,  and  two  of  them  are  equal  The  type'is  the  right  square  prism 
(g),  in  which  the  axes  join  the  centres  of  opposite  faces.  This  system 
includes  the  right  square  octahedron  (/). 


\ 


_t 


(<*)  («) 

3.  THE  ORTHORHOMBIC  SYSTEM  is  characterized  by  three  unequal 
axes  at  right  angles  to  each  other.  The  type  is  the  right  rectangular 
prism  (g),  in  which  the  axes  join  the  centres  of  opposite  faces.  By 
cutting  off  the  vertical  edges  until  the  new  plane  faces  meet,  the  right 


APPENDIX. 


343 


rho  nbic  prism  is  obtained.  Here  the  horizontal  axes  join  the  centres 
of  Apposite  edges,  while  the  vertical  axis  joins  opposite  facas.  The 
riglt  rhombic  octahedron  (h]  belongs  to  this  system. 


4 
pi  a 

Tli. 
poi 

and 


(9} 


THE  HEXAGONAL  SYSTEM  has  four  axes  ;  three  are  in  the  same 
ie,  and  would  join  the  opposite  angles  of  a  regular  hexagon. 

fourth  is  at  right  angles  to  these  three,  and  passes  through  their 
it  of  intersection.  The  hexagonal  prism  (i),  hexagonal  pyramid, 
rhombohedron  (j)  belong  to  this  system. 


(*)  0') 

5.  THE  CLINORHOMBIC  SYSTEM  has  three  axes,  all  of  which  are 
unequal  ;  two  of  them  are  inclined  to  each  other  and  in  the  same 
piano,  but  both  are  at  right  angles  to  the  third,  which  passes  through 
theiv  point  of  intersection.  The  right  rhomboidal  prism,  the  oblique 
rectangular  prism,  oblique  rhombic  prism,  and  oblique  rhombic  octa- 
hedron are  of  this  system. 

0.  THE  ANORTHIC  SYSTEM  has  three  unequal  axes,  neither  of  which 
is  at  right  angles  with  another.  The  oblique  rhomboidal  prism  is 
the  type  of  this  system. 

All  of  the  crystalline  forms  named  are  primitive  forms  ;  they  may 
be  modified  in  many  manners,  but  the  characteristic  axes  are  not 
affected  bv  the  modifications. 


344  APPENDIX. 

A  substance  which  crystallizes  in  forms  belonging  to  two  different 
systems  is  said  to  be  dimorphous.  Such  a  body  is  sulphur. 

Two  different  substances  whose  crystals  are  of  precisely  the  same 
form  are  said  to  be  isomorphous.  The  chlorides,  bromides,  and 
iodides  of  potassium  and  sodium  are  isomorphous :  the  alums  are  an 
excellent  example  of  isomorphous  compounds. 


HINTS  FOR  THE  PREPARATION  OF  EXPERIMENTS. 

Unless  the  floor  of  a  class-room  inclines  to  the  front,  the  table  on 
which  apparatus  is  arranged  and  experiments  performed  should  be 
quite  high.  A  table  closed  at  the  front  and  ends,  and,  with  the  ex- 
ception of  a  few  drawers,  entirely  open  at  the  back,  is  the  most  con- 
venient, as  a  large  quantity  of  apparatus  may  be  kept  ready  for  use 
under  it.  If  possible,  the  table  should  be  furnished  with  gas-  and 
water-pipes  having  several  taps,  and  these  are  most  convenient  if 
run  along  under  the  back  edge,  the  nozzles  of  the  taps  being  flush 
with  the  back.  A  water-supply  naturally  necessitates  a  sink  for  the 
waste-water,  and  this  may  well  be  set  in  the  table,  being  provided 
with  a  cover  pierced  with  holes  for  the  drainage  of  funnels,  con- 
densing apparatus,  etc.,  when  the  whole  surface  of  the  table  is  re- 
quired. 

A  pneumatic  trough  sunk  in  the  table  is  very  convenient  for  the 
teacher,  but  is  very  unsatisfactory  to  a  class  of  beginners,  who  desire 
to  see  every  process  of  manipulation.  It  is  therefore  much  better  to 
use  a  trough  entirely  of  glass,  and  nothing  answers  the  purpose  bet- 
ter than  a  strong  aquarium  trough  :  this  may  be  fitted  with  a  movable 
shelf,  suspended  from  the  edges  of  the  frame,  and  is  satisfactory  to 
teacher  and  pupils. 

All  the  apparatus  and  chemicals  required  for  ordinary  experiments 
should  be  kept  as  close  at  hand  as  possible,  and  ready  for  use ;  it  is 
advantageous,  when  possible,  to  use  the  same  set  of  apparatus  only  for 
the  same  experiment.  In  this  manner  the  time  required  for  me- 
chanical preparation  may  be  reduced  to  a  minimum,  and  in  case  of 
accident  any  part  of  an  apparatus  may  be  quickly  replaced. 

It  is  true  economy  to  provide  a  large  stock  of  flasks,  from  half-litre 
to  two  litres  capacity,  glass  tubing  of  all  sizes,  funnel-tubes,  beakers, 
and  rubber  tubing  and  corks.  Rubber  corks  may  be  obtained  pierced 
with  one,  two,  or  three  holes,  and  though  the  expense  of  a  stock  of 


APPENDIX.  345 

these  corks — say  half  a  dozen  of  each  useful  size — is  considerable  at 
fir.-t,  the  economy  of  time  which  would  otherwise  be  required  for 
fitting  and  boring  corks,  amply  repays  the  outlay.  The  rubber  corks 
made  by  Galante,  2  Rue  de  1'Ecole  de  Medecine,  Paris,  are  the  best, 
and  with  proper  care  may  be  used  several  years. 

J  f  rubber  corks  cannot  be  obtained,  ordinary  cork  may  be  bored 
by  cork-borers  or  by  a  red-hot  pointed  iron  wire.  The  hole  may  then 
be  enlarged  to  any  size  by  rat-tail  files.  Corks  should  be  adapted  by 
cu  ting  and  filing  to  fit  hermetically  without  the  use  of  sealing-wax 
or  luting  of  any  kind  :  a  sharp  shoemaker's  knife,  a  good  rasp,  and 
se\  eral  flat  files  are  required  for  this  purpose. 

Glass  flasks  and  porcelain  apparatus  should  not  be  heated  by  a 
na  ;ed  flame,  but  should  b^  placed  on  wire  gauze,  which  may  be  cut 
in!  >  squares  of  the  required  size,  and  its  use  enables  the  immediate 
application  of  heat  to  glass-ware  which  might  be  cracked  if  heated 
wi  hout  precaution. 

-Naturally,  gas  is  the  best  and  most  convenient  heating  agent,  but 
wl  en  this  cannot  be  obtained  it  is  in  most  cases  better  to  use  an  oil 
st(  v'e  than  a  spirit-lamp.  There  are  many  patterns  of  oil  stoves  in 
wl  ich  the  heated  gases  from  several  flames  may  be  entirely  employed 
in  very  little  space,  and  with  care  they  will  not  deposit  smoke  on 
apparatus  heated  over  them. 

A  blast-lamp  is  indispensable  for  the  operations  of  glass-working, 
an  1,  unless  gas  be  at  hand,  a  kerosene  lamp  with  a  large  loose  wick 
may  be  employed.  The  nozzle  of  the  blast  may  be  made  of  glass 
tul  o,  drawn  out  to  the  required  opening,  and  this  may  be  supported 
in  a  cork  which  can  be  raised  or  lowered  on  a  vertical  iron  rod. 
"When  gas  is  employed  for  the  blast-lamp,  a  single  flame  is  much 
more  satisfactory  in  the  laboratory  than  the  double  flame  generally 
employed  by  glass-blowers  in  this  country.  The  most  convenient  and 
cheapest  bellows  k  that  in  which  the  reservoir  is  a  caoutchouc  bag. 
It  is  durable,  and  can  be  adapted  to  all  laboratory  purposes  in  which  a 
blast  is  required. 

Glass  tubes  are  cut  by  notching  them  once  with  the  smallest-sized 
triangular  file,  firmly  grasping  each  end  between  the  thumb  and 
finger,  close  to  the  notch,  and  bending  from  the  filed  side.  The 
sharp  ends  may  then  be  rounded  by  holding  them  in  a  flame  until 
the  glass  begins  to  soften. 

The  art  of  glass-blowing  can  be  acquired  only  by  practice  ;  a  pound 
of  glass  tubes  and  a  few  hours  at  the  lamp  are  of  more  value  than 
ary  instruction.  The  beginner  must  learn  to  regulate  the  size  of  his 
flame  according  to  the  work  to  be  done,  to  heat  the  glass  evenly,  to 


346  APPENDIX. 

observe  the  moment  when  it  is  at  the  proper  temperature,  and  to 
remove  it  from  the  flame  before  bending,  drawing,  or  blowing. 

The  glass  must  be  hotter  for  bending  than  for  drawing,  and  hotter 
for  blowing  than  for  bending.  In  making  a  bend,  the  whole  length 
of  the  bend  should  be  uniformly  heated  by  holding  it  in  a  slanting 
position  through  the  flame,  and  rotating  it  slowly.  The  bend  should 
not  be  a  sharp  angle,  but  a  regular  curve.  To  blow  a  bulb,  the  glass 
should  be  somewhat  thickened  by  softening  the  portion  and  gently 
pressing  the  ends  towards  each  other.  If  the  bulb  is  to  be  on  the 
end  of  a  tube,  the  latter  will  be  sealed  and  shortened  by  the  cohesion 
of  the  softened  glass,  and  the  bulb  may  then  be.  blown  in  the  thick 
end.  Practice  and  patience  are  the  best  teachers. 

It  must  be  remembered  that  the  pupil's  interest  in  the  science  will 
depend  on  his  comprehension  of  the  facts,  and  all  apparatus  intended 
for  class-demonstration  should  be  large,  so  that  each  part  can  be  seen 
and  understood  by  every  pupil.  In  addition,  the  apparatus  should 
be  neatly  arranged  :  clumsy  contrivances  may  accomplish  results,  but 
they  often  fail  in  the  more  important  object  of  exhibiting  the  process 
to  which  the  result  is  due. 


INDEX. 


A  states,  210. 

Ac  ,1,  acetic,  C2H*02,  194,  207. 

acrylic,  C3H*02,  216. 

antimonic,  185. 

arsenic,  130. 

arsenious,  H3As03,  130. 

benzoic,  C7H<502,  231. 

boric,  H3B03,  138. 

butyric,  C*H802,  210. 

carbonic,  156. 

chloric,  HC103,  67. 

chromic,  326. 

citric,  C6H807,  219. 

cyanic,  HOCN,  172. 

digallic,  C"Hi»09,  233. 

ethylsulphuric,  C2H5.HS04,  203, 

formic,  CH8OS  168,  193,  207. 

gallic,  C7H605,  232. 

hydracrylic,  C3H«03,  216.    - 

hydriodic,  HI,  71. 

hydrobromic,  HBr,  69. 

hydrochloric,  HC1,  62. 

hydrocyanic,  HCN,  166. 
tests  for,  167. 

hydrofluoric,  HF1,  71. 

hydrofluosilicic,  H2SiFl6,  142. 

hypochlorous,  HC10,  65. 

hypophosphorous,  H3P02,  124. 

hyposulphurous,  H2S203,  81. 

isocyanic,  OCNH,  172. 

lactic,  C3H603,  216. 

lauric,  C12H2402,  215. 

malic,  C4H6Q5,  218. 

manganic,  H2Mn04,  323. 

margaric,  C«H3*02,  213. 

metaboric,  HBO2,  139. 

metantimonic,  HSbO3,  135. 


Acid,  inetaphosphoric,  HPO3,  127. 
.  metarsenic,  HAsO3,  130. 

myristic,  CUH2802,  215. 

nitric,  HNO3,  112. 

nitro-hydrochloric,  114. 

nitrous,  HNO2,  108. 

oleic,  C18H3<K)2,  213. 

ortharsenic,  H3AsO*,  130. 

orthophosphoric,  I13PO*,  125. 

oxalic,  C2H204,  216. 

palmitic,  C16113202,  212. 

permanganic,  H2Mn208,  324. 

phosphoric,  125. 

phosphorous,  H3P03,  125. 

picric,  C3H2(N02)3OH,  227. 

propionic,  C3H«02,  210. 

pyroantimonic,  H*Sbz07,  135. 

pyroarsenic,  H4As207,  130. 

pyrogallic,  C6H3(OH)3,  232. 

pyrophosphoric,  H4P207,  127. 

salicylic,  C6H4.OH(C02H),  232. 

silicic,  142. 

stannic,  330. 

stearic,  C18H3<502,  213. 

succinic,  C4H604,  218. 

sulphocarbonic,  H2CS3,  163. 

sulphuric,  H2SO*,  82. 
fuming,  H2S207,  81. 
molecular  structure  of,  85. 

sulphurous,  H2S03,  80. 

tannic,  233. 

tartaric,  C*H606,  218. 

tetraboric,  H2B*07,  139.n 

thiosulphuric,  H2S203,  81. 

uric,  C&H*N*03,  340. 

valeric,  C5Hi°02,  210. 
Acids,  51,  64. 

347 


348 


INDEX. 


Acids,  dibasic,  88,  216. 

fatty,  210,  212. 

of  carbon,  207. 
Acrolein,  C3H40,  210. 
Affinity,  13. 
Air,  92. 

carbon  dioxide  in,  95. 

water  in,  94. 
Alabaster,  89. 
Albite,  305. 
Albumen,  336. 
Albuminoid  substances,  335. 
Alcohol,  amyl,  C5H".OH,  198. 

benzyl,  C6H&.CH2OH,  230. 

butyl,  CW.OH,  198. 

ethyl,  C'lROH,  193. 
absolute,  194. 

methyl,  CH3.01I,  192. 

propyl,  C3H7.OH,  197. 
Alcoholic  beverages,  195. 
Alcohols,  192. 

diatomic,  199. 

primary,  197. 

secondary,  197. 

tertiary,  198. 

triatomic,  200. 
Aldehyde,  C2II40,  194,  206. 

ben  zoic,  CW.CHO,  231. 

salicylic,  C<4I4.OH.CHO,  231. 
Aldehydes,  206. 
Ale,  196. 
Alizarin,  190. 
Alkaloids,  236. 
Alloys,  242. 
Alumina,  AW,  303. 
Aluminium,  301. 

chloride,  A12C16,  302. 

hydrate,  A12(OH)6,  303. 

oxide,  A1203,  303. 

silicates,  305. 

sulphate,  A12(S04)3,  303. 

tests  for,  306. 
Alums,  304. 
Amalgams,  242. 
Amides,  173. 
Amines,  173,  229. 


Ammonia,  NH3,  97. 

analysis  of,  99. 

combustion  of,  99. 
Ammonium  alum,  304. 

amalgam,  103. 

carbonates,  161. 

chloride,  NH*C1,  101. 

compounds,  100. 

dichromate  (NH4)2Cr20T,  327. 

isocyanate,  NH*NCO,  172. 

nitrate,  NH*.N03,  104. 

oxalate  (NH4)2C204,  117. 

picrate,  NH4.OC6H2(N02)3,  228. 

sulphate  (NH4,2S04,  102. 

sulphide  (NH*)2S,  102. 

sulphocyanate,  NH*NCS,  175. 

sulphydrate,  NH4SH,  102. 
Amygdalin,  231. 
Amyl  acetate,  C5HU.C2H302,  212. 

alcohols,  CSIin.OH,  198. 
Amylene,  C5H10,  185. 
Analysis,  33. 

of  carbon  compounds,  190. 
Anatase,  331. 
Anglesite,  91. 
Aniline,  C6R5.NH2,  228. 

colors,  230. 

Anthracene,  C14H10,  190. 
Anthracite,  145. 
Antichlor,  81. 

Antimonio-potassium  tartrate,  219. 
Antimony,  134. 

chlorides,  135. 

oxides,  135. 

trisulphide,  135. 
Apatite,  127. 
Aragonite,  160. 
Aromatic  compounds,  189. 
Arsenic,  128. 

chloride,  AsCl3,  129. 

disulphide,  As2S2,  130. 

pentoxide,  As205,  130. 

tests  for,  131. 

trioxide,  As203,  129-. 

trisulphide,  As2S3,  130. 
Arsenic  oxide,  As205,  130. 


INDEX. 


349 


Arsonious  oxide,  As203,  129. 
Atazamite,  288. 
Ah  losphere,  92. 
Atomic  heats,  250. 

theory,  40. 

weights,  determination  of,  41. 
Atomicity,  theory  of,  71,  78,  86,  110, 

1  56,   163,   178,   187,  197,  205,  245, 

2  i7,  265,  272,  287,  291,  302. 
Atr  >pine,  C17H23N03,  239. 

Au  ic  chloride,  AuCl3,  300. 
A\T"gadro's  law,  39. 
Azi;rite,  289. 

Bai  ium,  270. 

carbonate,  BaCO3,  160. 

chloride,  BaCl2,  270. 

dioxide,  BaO2,  271. 

monoxide,  BaO,  270. 

nitrate,  Ba(N03)2,  118. 

sulphate,  BaSO4,  89. 

sulphide,  BaS,  270. 

tests  for,  271. 
Bee  r,  196. 
Bel  -metal,  287. 
Bei  zine,  182. 
Bei  zol,  C«H6,  187. 

derivatives,  226. 
Bei  zyl  alcohol,  C«H*.CH2OH,  230. 

aldehyde,  C6ERCHO.  230. 

chloride,  C6H5.CH2C1,  231. 
Beryl,  277. 
Bismuth,  295. 

chloride,  BiCl3,  296. 

nitrate,  Bi(N03)3,  296. 

oxide,  Bi203,  296. 

sulphide,  Bi2S3,  296. 

tests  for,  297. 
Bitter  almond  oil,  231. 
Bituminous  coal,  145. 
Blende,  278,  282. 
Blue  vitriol,  CuSO4,  90. 
Borax,  Na'B^O7, 139. 
Borneol,  C10H180,  235. 
Boron,  137. 

chloride,  BC13,  13&. 


Boron,  crystallized,  138. 

oxide,  B203,  137. 

tests  for,  140. 
Brandy,  196. 
Brass,  287. 
Braunite,  322. 
Bromides,  248. 
Bromine,  68. 
Bromoform,  CllBr3,  206. 
Bronze,  287. 
Brookite,  331. 
Brucine,  240. 
Bunsen  burner,  31. 
Butyl  alcohols,  C4IP.OH,  198. 
Butylenes,  C4H8,  185,  186. 

Cacodyl,  As2(CR3)4,  210. 
Cadmium,  283. 

ferrocyanide,  Cd2(FeC6N6),  283. 

iodide*  CdP,  283. 

oxide,  283. 

sulphide,  CdS,  283. 

tests  for,  283. 
Caesium,  257, 
Caffeine,  C8Hi°:NT402,  238. 
Calamine,  160,  278. 
Calcite,  160. 
Calcium,  265. 

carbonate,  CaCO3,  160. 

in  hard  water,  49,  156. 

chloride,  CaCl2,  265. 

citrate,  220. 

hydrate,  Ca(OH)2,  267. 

hypochlorite,  Ca(ClO)2,  66. 

lactate,  Ca(C3H503)2,  216. 

phosphates,  126. 

phosphide,  123. 

sulphate,  CaSO4,  89. 
in  hard  water,  49. 

tests  for,  269. 
Calomel,  Hg2Cl2,  292. 
Camphol,  C^H^O,  234. 
Camphors,  234. 
Cane  sugar,  C12H220'i,  224. 
Caramel,  225. 
Carbamide,  CO(NH2)2,  173. 


30 


350 


INDEX. 


Carbon,  144. 

atomicity  of,  163. 

compounds,  analyses  of,  190. 

dioxide,  CO2,  153. 
in  air,  95. 
test  for,  156. 

disulphide,  CS2,  162. 

hydrates  of,  220. 

monoxide,  CO,  150. 

compounds  of,  171. 

oxysulphide,  COS,  164. 

reduction  by,  150. 
Carbonates,  156. 

test  for,  157. 
Carbonyl  amide,  CO(NH2)2,  173. 

chloride,  COC12,  153. 

compounds  of,  171. 
Carboxyl,  207. 
Case-hardening,  314. 
Casein,  338. 
Cassiterite,  328. 
Celestine,  89,  269. 
Cellulose,  C6Hi°05,  222. 

nitro-,  223.     ' 
Cement,  267. 
Cerium,  306. 
Chalkosine,  284. 
Champagne,  196. 
Charcoal,  147. 

absorbent  properties  of,  149. 

animal,  147. 

filter,  149. 
Chemical  affinity,  13. 

changes,  8. 

combination,  11. 

energy,  152. 

equations,  42. 

formulae,  42. 

laws  and  theories,  35,  38. 

nomenclature,  50,  61,  66. 

notation,  42. 
Chloral,  C2C13HO,  207. 
Chlorates,  66. 
Chlorides,  61,  248. 

test  for,  62. 
Chlorine,  67. 


Chlorine,  analogies  with  bromine  and 

iodine,  71. 

Chloroform,  CHC13,  206. 
Chromates,  326. 

test  for,  328. 
Chrome  green,  325. 

yellow,  327. 
Chromite,  325. 
Chromium,  325. 

chlorides,  325. 

oxides,  325. 
Cinchona  bark,  239. 
Cinchoninc,  240. 
Cinnabar,  200,  294. 
Clay,  305. 
Coal,  145. 

-mine  explosions,  176. 
Coal  tar,  187. 
Cobalt,  319. 

blue,  ?20. 

chloride,  CoCl2,  319. 

oxides,  319. 

tests  for,  320. 
Cocaine,  239. 
Codeine,  239. 
Colcothar,  317. 
Collodion,  223. 
Combination,  laws  of,  35,  38. 
Combustion,  26. 

slow,  31. 
Compounds,  9. 
Conine,  C8Hi5N,  237. 
Copper,  283. 

acetate,  Cu(C2H302)2,  210. 

action  of  ammonia,  287. 

alloys  of,  287. 

arsenite,  CuHAsO3,  132. 

atomicity  of,  287. 

carbonates,  289. 

cement,  286. 

chlorides,  287. 

metallurgy  of,  284. 
wet  process,  285. 

nitrate,  Cu(N03)2,  118. 

oxides,  289. 

sulphate,  CuSO*,  90. 


INDEX. 


351 


Copper  sulphides,  289. 

tests  for,  289. 
Copperas,  FeSO4,  90. 
Coirosive  sublimate,  HgCl2,  292. 
Cu  undum,  APO3,  303. 
Ci  «  am,  339. 
Cnain  of  tartar,  219. 
Or-  sols,  230. 
Ci    olite,  72. 
Cr   stallization,  341. 

water  of,  47. 
Cr  stallography,  341. 
Ci;  >ellation,  259. 
Cuuric  chloride,  CuCl2,  288. 

ferrocyanide,  Cu2(FeC6N6),  289. 

nitrate,  Cu(N03)2,  118. 

oxide,  CuO,  288. 

sulphate,  CuSO4,  90. 

sulphide,  CuS,  288. 
Ci.orous  chloride,  Cu2Cl2,  288. 

oxide,  Cu20,  288. 

sulphide,  Cu2S,  289. 
Cy  mogen,  (CN)2,  164. 

molecular  structure  of,  165. 
Cy  nene,  C^IH4,  234. 


Da.  ton's  law,  36. 
D;nurine,  C^H^NO8,  239. 
Decomposition,  11. 

double,  15. 

Definite  proportions,  laws  of,  36. 
Dectrin,  222. 
Di;  lysis,  142. 
Diamond,  144. 
Dijistase,  222,  339. 
Duiyinium,  306. 
Digestion,  339. 
Diiaethylamine,  229. 
Dimorphism,  75,  343. 
Dynamite,  200. 

Elements,  9. 

table  of,  44. 
Elutriation,  282. 
Emerald,  277. 
Emery,  303. 


j  Epsom  salt,  MgSO4,  90. 
1  Equivalent  combining  proportions,  38. 
Erbium,  306. 
Ethane,  C2H6,  179. 
Ether,  (C2H5)20,  201. 
Ethers,  compound,  211. 

simple,  201. 
Ethyl  acetate,  C2H5.C2H302,  211. 

bromide,  C2H&Br,  205. 

formate,  C2H5.CH02,  212. 
.  hydrate,  C2H5.0H,  193. 

iodide,  C2H5J,  204. 

nitrate,  C2H5.N03,  211. 

oxide,  (C2H5)20,  201. 

valerate,  C2H5.C5H9Q2,  212. 
Ethylene,  C2H*,  184. 

bromide,  C2H4Br2,  185. 

chloride,  C2H4C12,  184. 

cyanide,  C2H*(CN)2,  218. 

hydrate,  C2H*(OH)2,  199. 

oxide,  C2H*0,  204. 
Ethylidene  bromide,  C2H4Br2,  206. 

Fats,  natural,  213. 
Feldspar,  305. 
Fermentation,  acetic,  209. 

alcoholic,  193. 
Ferric  chloride,  Fe2Cl6,  316. 

ferrocyanide,  Fe*(FeC6N6)3,  170. 

oxide,  Fe203,  317. 

sulphate,  Fe2(S04)3,  318. 
Ferrocyanides,  169. 
Ferrous  carbonate,  FeCO3,  160. 

chloride,  FeCl2,  316. 

ferricyanide,  Fe3(FeC6N6)2,  171. 

oxide,  FeO,  316. 

sulphate,  FeSO4,  90. 
Fibrin,  337. 
Fire,  29. 
Fire-damp,  176. 
Fireworks,  271. 
Flame,  30,  176. 
Fluorine,  71. 
Fluor-spar,  CaFl2,  72. 
Formates,  208. 
Formulae,  chemical,  42. 


352 


INDEX. 


Fractional  distillation,  187. 
Fuller's  earth,  305. 
Fulminates,  195. 
Fusible  metal,  296. 

Gallium,  306. 
Gas-carbon,  147. 
Gas,  illuminating,  145. 
Gases,  manipulation  of,  20. 

molecular  volumes  of,  39. 
Gas  liquor,  101,  147. 
Gasoline,  182. 
Gay-Lussac's  laws,  36,  38. 
Gelatin,  339. 

Gelatinoid  substances,  335. 
German  silver,  287,  321. 
Gilding,  300. 
Gin,  197. 
Giobertite,  160. 
Glass,  141. 

etching  on,  71. 
Glucinum,  277. 
Glucose,  C«H1206, 193,  223. 
Glue,  339. 
Gluten,  220,  336. 
Glycerin,  C3H5(OH)3,  199. 

ethers  of,  213. 
Glycol,  C2H*(OH)2,  199. 
Glycols,  198. 
Goethite,  307,  317. 

Gold,  297. 

assay,  300. 
chlorides,  299. 
hydraulic  mining  of,  298. 
oxides,  300. 

Granite,  305. 

Graphite,  144. 

Green  vitriol,  FeSO4,  90. 

Gum  arabic,  226. 

Gun-cotton,  222. 

Gun  metal,  287. 

Gunpowder,  117. 

Gypsum,  89. 

Hausmannite,  322. 
Heat  of  combustion,  152. 


Heavy  spar,  BaSO4,  89,  270. 
Helium,  245. 
Hematite,  307. 
Hemoglobin,  337. 
Holmium,  306. 
Homologous  bodies,  181. 
Horn  silver,  261. 
Hydrates,  51,  246. 

of  carbon,  220. 
Hydrocarbons,  OH2n+2,  178. 

nomenclature  of,  180,  183. 

unsaturatcd,  183. 

OH2",  185. 
Hydrogen,  16. 

absorption  by  palladium,  22,  334. 

antimonide,  SbH3,  136. 

arsenide,  AsH3,  132. 

conductibility  for  heat,  21. 

diffusion  of,  19. 

dioxide,  55. 

phosphide,  PH3,  122. 

sulphide,  H2S,  75. 
analysis  of,  77. 
as  reagent,  77. 
Hydroxyl,  65. 
Hypochlorites,  66. 
Hypochlorous  oxide,  01*0,  65. 

Iceland  spar,  160. 
Illuminating  gas,  145. 
Indigo,  C16H10N202,  235. 

white,  C16H12N202,  236. 
Indium,  300. 
Ink,  233. 

sympathetic,  320. 
Iodides,  248. 
Iodine,  69. 

test  for,  71. 
lodoform,  CHI3,  206. 
Iron,  307. 

blast-furnace  process,  308. 

bloom,  310. 

carbonate,  FeCO3,  160. 

cast,  311. 

Catalan  process,  307. 

chlorides,  316. 


INDEX. 


353 


Iron,  galvanized,  281. 

gray,  311. 

oxides,  316,  317. 

passive,  316. 

pig,  310. 

pyrites,  74,  318. 

soft,  315. 

sulphates,  90,  318. 

sulphides,  317. 

tests  for,  318. 

white,  311. 

Is<  inerism,  172,  186,  197. 
Is<  inorphisin,  90,  343. 

Je  ,  147. 

K;  >lin,  305. 
Kt  -osene,  182. 
Ki  'serite,  277. 
Ki  pfernickel,  320. 

Lit  >radorite,  305. 

La  :tose,  C12H'"On,  225. 

La  up-black,  148. 

La  ithanum,  306. 

La  ighing-gas,  N20,  104. 

La  v  of  Avogadro  and  Ampere,  39. 

of  definite  proportions,  36. 

of  Gay-Lussac,  36,  38. 
Lend,  272. 

acetate,  Pb(C2H302)2,  210. 

carbonate,  PbCO3,  160. 

chloride,  PbCl2,  274. 

chromate,  PbCrO4,  327. 

cupellation  of,  259. 

dioxide,  PbO2,  275. 

iodide,  Pbl2,  274. 

monoxide,  PbO,  275. 

nitrate,  Pb(N03)2,  118. 

poisoning  by,  274. 

red  oxide,  Pb30*,  275. 

sulphate,  PbSO4,  91. 

sulphide,  PbS,  276. 

tests  for,  276. 
Legumine,  336. 
Lepidolite,  250. 

x 


Levulose,  C6H120<5,  225. 
Life,  chemistry  of,  334. 
Lignite,  147. 
Lime,  CaO,  266. 

chlorinated,  CaCl(ClO),  66,  268. 
Lithium,  250. 
Lixiviation,  159. 

Magnesia,  MgO,  278. 

white,  160. 
Magnesite,  160,  277. 
Magnesium,  277. 

carbonate,  MgCO3,  160. 

chloride,  MgCl2,  277. 

citrate,  220. 

hydrate,  Mg(OH)2,  278. 

oxide,  MgO,  278. 

sulphate,  MgSO*,  90. 

tests  for,  278. 
Malachite,  289. 
Malt,  193. 

Maltose,  C6H1206,  196,  224. 
Manganese,  322. 

dioxide,  MnO2,  322. 

oxides,  322. 

sulphide,  MnS,  324. 

tests  for,  324. 

Margarin,  GSRS^'H^O2)3,  213. 
Marl,  305. 
Marsh  gas,  178. 
Marsh's  test  for  arsenic,  133. 
Matches,  121. 
Meadow-sweet  oil,  231. 
Menthol,  C1°H200,  235. 
Mercuric  chloride,  HgCl2,  292. 

cyanide,  Hg(CN)2,  169. 

iodide,  Hgl2,  293. 

nitrate,  Hg(N03)2,  118. 

oxide,  HgO,  293. 
Mercurous  chloride,  Hg'Ci2,  292. 

iodide,  Hg2!2,  293. 

oxide,  Hg20,  293. 
Mercury,  290. 

atomicity  of,  291. 

chloride,  292. 

cyanide,  169. 
30* 


354 


INDEX. 


Mercury,  fulminate,  195. 

molecular  weight  of,  291. 

oxides,  293. 

sulphide,  294. 

tests  for,  29-1. 
Metallic  bromides,  248. 

carbonates,  156. 

chlorides,  61,  248. 

hydrates,  52,  246. 

nitrates,  115,  116. 

oxides,  246. 

sulphates,  87. 
Metals,  15. 

general  properties  of,  241. 

natural  state  of,  242. 
Methane,  CH*,  1 75. 
Methylamino,  CH3.NH2,  229. 
Methylaniline,  CI18.C6H«N,  229. 
Methylbenzol,  CH3.C6H5,  189. 
Methyl  chloride,  CH3C1,  204. 

cyanide,  CH3CN,  210. 

hydrate,  CH3.OH,  192. 

iodide,  CH3I,  178. 

oxide,  (CH3)20,  201. 

salicylate,  CH3.C'H503,  232. 
Mica,  305. 
Milk,  338. 
Mineral  waters,  49. 
Mispickel,  128. 
Molecular  weights,  determination  of, 

40. 

Molecules,  IT. 
Molybdenite,  328. 
Molybdenum,  328. 
Morphine,  C^H^NO3,  329. 
Myosin,  337. 

Naphtha,  182. 
Naphthaline,  C10H8,  189. 
Narcotine,  C22H23NO?,  239. 
Nessler's  reagent,  293. 
Nickel,  320. 

chloride,  NiCl2,  322. 

oxides,  322. 

plating,  321. 

sulphate,  NiSO4,  322. 


Nickel,  tests  for,  322. 
Nicotine,  C^H^N2,  238. 
Niobium,  136. 
Nitrates,  115,  116. 
Nitric  oxide,  NO,  106. 
Nitrobenzol,  C6H5.N02,  228. 
Nitrogen,  91. 

atomicity  of,  110. 

dioxide,  NO,  106. 

group  of  elements,  136. 

iodide,  103. 

monoxide,  N20,  104. 

pentoxide,  N205,  110. 

peroxide,  NO2,  108. 

trioxide,  N203,  109. 
Nitroglycerin,  C3H5(N03)3,  200. 
Nitrosyl  chloride,  NOC1,  108. 
N  trotoluols,  C6H4(CH3)N02,  229. 
Nitrous  oxide,  N20,  104. 
Nitryl  chloride,  N02C1,  109. 
Nomenclature  of  acids  and  salts,  66. 

of  chlorine  compounds,  61. 

of  oxygen  compounds,  50. 
Notation,  42. 

Oil*,  essential,  189. 

fatty  and  drying,  214. 
Olein,  C3H5(C18H3302)3,  214. 
Oolite,  307. 
Opium,  239. 
Orpiment,  As2S3,  130. 
Orthophosphates,  126. 
Osmium,  334. 
Oxalates,  217. 
Oxides,  50,  246. 
Oxygen,  23. 

in  air,  92. 

manufacture  of,  323. 

properties  of,  26. 
Oxyhydrogen  blow-pipe,  29. 
Ozone,  53. 

Palladium,  333. 

Palmitine,  C3H5(C16H3102)3,  213. 

Paraffin,  182. 

Paris  green,  133. 


INDEX. 


355 


Pepsin,  339. 
Petroleum,  181. 
Pewter,  274. 
Ph.-nol,  C6H5.0H,  226. 

nitro-,  227. 

test  for,  227. 
Ph'.sphorus,  119. 

amorphous,  121. 

chlorides,  123. 

oxides,  123. 
Ph  tography,  264. 
Ph  -sical  changes,  7. 
Pit  ihblende,  325. 
Plater  of  Paris,  89. 
Phitinum,  332. 

black,  333. 

chlorides,  333. 

sponge,  332. 
PI  i  tnbago,  144. 
Po  ymerism,  185. 
Po  ter,  196. 
Po:  issium,  254. 

acid  carbonate,  KHCO3,  160. 

acid  tartrate,  KC4I1506,  219. 

alum,  304. 

bromide,  KBr,  256. 

carbonate,  K2C03,  159. 

chlorate,  KCIO3,  69. 

chloride.  KC1,  256. 

chromate,  K2Cr04,  326. 

cyanate,  KOCN,  172. 

cyanide,  KCN,  168. 

dichromate,  K2Cr207,  326. 

ferricyanide,  R6(FeC6N6)2,  170. 

ferrocyanide,  K*FeC6N6,  169. 

hydrate,  KOH,  255. 

hypochlorite,  KCIO,  66. 

iodide,  KI,  256. 

isocyanate,  KNCO,  171. 

manganate,  K2Mn04,  323. 

nitrate,  KNO3,  116. 

oxide,  K20,  254. 

permanganate,  K2Mn208,  324. 

picrate,  KO.C6112(N02)3,  228. 

-sodium  tartrate,  219. 

sulphate,  R2S04,  89. 


Potassium  sulphocyanate,  KNCS,  174. 

sulphydrate,  KSH,  78. 

tartrate,  K2C4H406,  219. 

tests  for,  256. 
Pottery,  305. 
Propane,  C3H8,  1 79. 
Propyl  alcohols,  C3IROH,  197. 
Propylene,  C3H6,  185,  186. 
Prussian  blue,  170. 
Ptyalin,  339. 
Pur,ple  of  Cassius,  300. 
Pyrites,  copper,  284. 

iron,  318. 

Pyrogallol,  C6H3(OH)3,  232. 
Pyrolusite,  322. 

Quinine,  C20H2*N202,  239. 
sulphate,  240. 

Radicals,  87. 

acid  and  basic,  103. 

hydrocarbon,  178. 
hydrates  of,  192. 
oxides  of,  201. 
Realgar,  As2S2,  130. 
Red  precipitate,  293. 
Reinsch's  test  for  arsenic,  131. 
Respiration,  32. 
Rhodium,  334. 

Rochelle  salt,  KNaC4H<0«,  219. 
Rosaniline,  C»Hi»N»,  229. 
Rubidium,  257. 
Ruby,  304. 
Rum,  197. 
Rust,  315,  317. 
Ruthenium,  334. 
Rutile,  330. 

Saccharose,  C»H»0»,  224. 
Safety-lamp,  176. 
Salts,  65. 

neutral  and  acid,  88. 
Samarium,  306. 
Saponification,  214. 
Sapphire,  304. 
Scandium,  306. 


356 


INDEX. 


Scheele's  green,  133. 

Sea- water,  253. 

Selenite,  89. 

Selenium,  87. 

Serpentine,  277. 

Shot,  129,  274. 

Siemens'  regenerative  furnace,  279. 

Silica,  SiO2,  140. 

Silicon,  140. 

oxide,  SiO2,  140. 
Silver,  257. 

arsenate,  Ag3AsO*,  130,  133. 

arsenite,  Ag2HAs03,  132. 

assay,  262. 

chloride,  AgCl,  261. 

chromate,  Ag2OO*,  262. 

cyanide,  AgCN,  168. 

iodide,  Agl,  262. 

nitrate,  AgNO3,  118. 

oxide,  Ag20,  261. 

sulphide,  Ag2S,  262. 

tests  for,  262. 
Silvering,  262. 
Slow  combustion,  31. 
Soap,  214. 

salt  water,  215. 
Soapstone,  277. 
Soda-water,  154. 
Sodium,  251. 

acetate,  NaC2H302,  210. 

acid  carbonate,  NaHCO3,  158. 

acid  sulphate,  NaHSO*,  88. 

alum,  304. 

borates,  137,  139. 

carbonate,  Na2C03,  157. 

chloride,  NaCl,  253. 

hydrate,  NaOH,  252. 
hypochlorite,  NaCIO,  66. 
hyposulphite,  Na2S203,  81. 
methylate,  NaCH30,  193. 
nitrate,  NaNO3,  116. 
oxide,  Na20,  253. 
phosphates,  126. 
•potassium  tartrate,  219. 
sulphate,  Na2S04,  88. 
sulphite,  Na2S03,  80. 


Sodium,  tests  for,  254. 

tetraborate,  Na2B*07,  139. 

thiosulphate,  Na2S203,  81. 
Solder,  274. 
Spathic  iron,  160. 
Specific  heat,  249. 
Spectrum  analysis,  242. 
Speculum  metal,  287. 
Speiss,  320. 
Spiegeleisen,  311. 
Stannic  chloride,  SnCl4,  330. 

oxide,  SnO2,  330. 
Stannous  chloride,  SnCl2,  330. 

oxide,  SnO,  330. 
Starch,  220. 
Stearin,  C3H5(C18H3502)3,  213. 

candles,  214. 
Steel,  311. 

Bessemer  process,  312. 

tempering,  313. 
Strontianite,  160,  269. 
Strontium,  269. 

carbonate,  SrCO3,  160. 

chloride,  SrCl2,  269. 

dioxide,  SrO2,  270. 

monoxide,  SrO,  270. 

nitrate,  Sr(N03)2,  118. 

sulphate,  SrSO4,  89. 

sulphide,  SrS,  269. 

tests  for,  270. 

Strychnine,  C21H22N202,  240. 
Substance,  definition,  7. 
Sugar,  cane,  C12H220",  224. 

grape,  C6H1206,  223. 

milk,  C12H22On.  225. 

of  lead,  Pb(C2H302)2,  210. 
Sulphates,  87. 

test  for,  88. 
Sulphides,  73,  248. 

tests  for,  75. 
Sulphites,  80. 

Sulpho-urea,  CS(NH2)2,  175. 
Sulphur,  73. 

atomicity  of,  86. 
dimorphism  of,  75. 
dioxide,  SO2,  79. 


INDEX. 


357 


Sulphur,  soft,  74. 

trioxide,  SO3,  81. 
Si  Iphuryl  chloride,  SOW,  86. 
Si  Iphydrates,  78. 
Synthesis,  33. 

Tannin,  233. 

Tsmning,  233. 

Ts  ntalum,  136. 

T!  rtar-emetic,  K(SbO)C4H406,  219. 

T:  rtrates,  219. 

Tellurium,  87. 

Tl  allium,  300. 

Tl.eine,  CPHWIW,  238. 

Tl  oobroinine,  C7H8N402,  238. 

Tl  iosulphates,  81. 

Tl  ulium,  306. 

Tl  ymol,  C10H140,  234. 

Ti  i,  328. 

dichloride,  SnCl2,  329. 

oxides,  330. 

sulphides,  330. 

tests  for,  331. 

tetrachloride,  SnCl4,  330. 
Titanium,  331. 
Toluol,  C6H5.CH3,  189. 
Topaz,  304. 

Triahloraldehyde,  C2C13HO,  207. 
Tri  nethylamine,  (CH3)3N,  229. 
Trinitrophenol,  C6H2(N02)3OH,  227. 
Tungsten,  328. 
Tumbull's  blur,  171. 
Turpentine,  C10!!^,  189. 
Type-metal,  135. 

Uranium,  325. 
Urea,  CO(NH2)2,  172. 

molecular  structure  of,  173. 

nitrate,  CO(NH2)2HN03,  174. 

Vanadium,  136. 


Verdigris,  210,  286. 
Vermilion,  294. 
Vinegar,  209. 
Vitriol,  blue,  CuSO4,  90. 

green,  FeSO4,  90. 

oil  of,  H2S04,  83. 

white,  ZnSO4,  90. 

Water,  32. 

electrolysis  of,  33. 
*  hard,  48. 

in  air,  94. 

mineral,  49. 

natural,  48. 

of  crystallization,  47. 

properties  of,  45,  47. 

synthesis  of,  34. 
Water-gas,  153. 
Whiskey,  196. 
White  lead,  160. 
White  vitriol,  ZnSO4,  90. 
Wine,  196. 
Wintergreen  oil,  232. 
Witherite,  160,  270. 
Wolfram,  328. 
Wood-spirit,  192. 

Yeast,  194. 
Yttrium,  306. 

Zinc,  278. 

carbonate,  ZnCO3,  160. 

chloride,  ZnCl2,  281. 

ferrocyanide,  Zn2,FeC6N6),  282. 

oxide,  ZnO,  282. 

sulphate,  ZnSO4,  90. 

sulphide,  ZnS,  282. 

tests  for,  282. 

white,  ZnO,  282. 
Zirconium,  330. 


THE    END. 


PUBLICATIONS   OF  J.  B.  LIPPINCOTT  &»    CO. 


THE  READERS  FOR   YOUR  SCHOOLS. 


UPPIIVCOTT'S 

POPULAR  SERIES  OF  READERS. 

By    MARCIUS     WILLSON. 


1  60  pages. 
228  pages. 
334  pages. 
480   pages. 
544  pages. 

I2mo. 
I2mo. 
I2mo. 
1  2mo. 
I2mo. 

Half 
Half 
Hall- 
Cloth 
Cloth 

THIS  SERIES  OF  READERS  EMBRACES  SIX  BOOKS,  AS  FOLLOWS i 
FIRST  READER.    With  Illustrations. "  96  pages.    I2mo.     Half  bound. 

20  cents.f 
SECOND  READER.     With  Illustrations. 

bound.     33  cents.f 
THIRD  READER.     With  Illustrations. 

bound.     44  cents.f 
FOURTH   READER.     With  Illustrations. 

bound.     60  cents.f 
FIFTH  READER.     With  Illustrations. 

sides.     90  cents.f 
SIXTH   READER.     With  Frontispiece. 

sides.     $i.oo.f 

They  combine  the   greatest  possible   interest  with  appro- 
priate instruction. 

They  contain  a  greater  variety  of  reading   matter  than  is 
usually  found  in  School  Readers. 

They  are  adapted  to  modern  methods  of  teaching. 
They  are  natural  in  method,  and  the  exercises  progressive. 
They  stimulate  the  pupils  to  think  and  inquire,  and  there- 
fore interest  and  instruct. 

They  teach  the  principles  of  natural  and  effective  reading. 
The  introduction  of  SCRIPT  EXERCISES  is  a  new  fea- 
ture, and  highly  commended  by  teachers. 

The  LANGUAGE  LESSONS  accompanying  the  exercises 
in  reading  mark  a  new  epoch  in  the  history  of  a  Reader. 

The  ILLUSTRATIONS  are  by  some  of  the  best  artists, 
and  represent  both  home  and  foreign  scenes. 


"  No  other  series  is  so  discreetly 
graded,  so  beautifully  printed,  or  so 
philosophically  arranged."  — Albany 
Journal. 

"  We  see  in  this  series  the  beginning 
of  a  better  and  brighter  day  for  the 
reading  classes." — New  York  School 
Journal. 


"The  work  may  be  justly  esteemed 
as  the  beginning  of  a  new  era  in  school 
literature." — Baltimore  News. 

"  In  point  of  interest  and  attractive- 
ness the  selections  certainly  surpass  any 
of  the  kind  that  have  come  to  out 
knowledge."—  The  Boston  Sunday 
Globe. 


The  unanimity  with  which  the  Educational  Press  has  commended 
the  Popular  Series  of  Readers  is,  we  believe,  without  a  parallel  in 
the  history  of  similar  publications,  and  one  of  the  best  evidences  that 
the  books  meet  the  wants  of  the  progressive  teacher. 


PUBLICATIONS   OF  J,  B.  LIPPINCOTT  &*   CO. 


THE    STANDARD    DICTIONARY 

OF  THE   ENGLISH    LANGUAGE. 


Worcester's  Unabridged 

QUARTO   DICTIONARY. 

EDITION,   WITH 


Fully  Illustrated.    With  Four  Full-page  Illuminated  Plates.     Library 
Sheep,  Marbled  Edges.    $10.00. 

RECOMMENDED  BY  THE  MOST  EMINENT  WRITERS. 

ENDORSED  BY  THE  BEST  AUTHORITIES. 


THE   NEW    EDITION    OF 

ST:E:R,'S   ZDiOTi 

Contains  Thousands  of  Words  not  to  be  fonnd  in  any  other  Dictionary. 


THE    COMPLETE    SERIES    OF 

WORCESTER'S    DICTIONARIES. 

QUARTO  DICTIONARY.  Profusely  Illustrated.  Library  sheep.  #10.00. 
ACADEMIC  DICTIONARY.  Illustrated.  Crown  8vo.  Half  roan.  Ji.go.f 
COMPREHENSIVE  DICTIONARY.  Illustrated.  i2mo.  Halfroan.  #i.4o.f 
NEW  COMMON  SCHOOL  DICTIONARY.  Illustrated.  i2mo.  Half 

roan.     90  cents. f 

PRIMARY  DICTIONARY.      Illustrated.     i6mo.     Halfroan.     48  cents.f 
POCKET    DICTIONARY.      Illustrated.      24mo.      Cloth.     50  cents.f    Roan, 

flexible.     69  cents.f    Roan,  tucks,  gilt  edges.     78  cents.f 


UNIVERSITY  OF   CALIFORNIA  LIBRARY 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


I 


DEC  IV1- 
NOV    3   1915 


30m-6/14 


VB  17066 


237556 


